| Task | Required Privilege Class |
|---|---|
| Define device classes | System or unrestricted storage |
You can define multiple device classes for each device type. For example, you may need to specify different attributes for two different storage pools that use the same type of tape drive. Variations may be required that are not specific to the device, but rather to how you want to use the device (for example, mount retention or mount limit).
If you are using device classes that have any of the following device types, you must define libraries and drives to the ADSM server before you define device classes to access your sequential media:
See Chapter 7. "Defining Drives and Libraries".
If you include the DEVCONFIG option in the dsmserv.opt file, the files you specify with that option are automatically updated with the results of this command. When you use this option, the files specified are automatically updated whenever a device class, library, or drive is defined, updated, or deleted.
The following sections explain the device classes for each supported device type.
To use tape devices, you must define a device class by issuing a DEFINE
DEVCLASS command with the DEVTYPE parameter.
| Device | ADSM Device Type |
|---|---|
| 4mm | 4MM |
| 8mm | 8MM |
| Digital linear tape | DLT |
| Digital tape format | DTF |
| Quarter-inch tape | QIC |
| IBM 3570 | 3570 |
| IBM 3590 | 3590 |
| IBM 34xx | CARTRIDGE |
| AIX-supported tape devices | GENERICTAPE |
| StorageTek tape devices | ECARTRIDGE |
Other parameters specify how to manage data storage operations involving the new device class:
You can update the device class by issuing the UPDATE DEVCLASS command.
You can limit the number of drives that the device class has access to at one time with the MOUNTLIMIT parameter.
The default mount limit value is DRIVES. The DRIVES parameter indicates that every time a mount point is allocated, the number of drives online and defined to the library is used to calculate the true mount limit value. The maximum value for this parameter is 256 and the minimum value is 0. A zero value prevents new transactions from gaining access to the storage pool.
When selecting a mount limit for a device class, be sure to consider the following questions:
Do not specify a mount limit value that is greater than the number of associated available drives in your installation. If the server tries to mount as many volumes as specified by the mount limit and no drives are available for the required volume, an error occurs and client sessions may be terminated. (This does not apply when the DRIVES parameter is specified.)
ADSM automatically cancels some processes to run other, higher priority processes. If the server is using all available drives in a device class to complete higher priority processes, lower priority processes must wait until a drive becomes available. For example, ADSM cancels the process for a client backing up directly to tape if the drive being used is needed for a server migration or tape reclamation process. ADSM cancels a tape reclamation process if the drive being used is needed for a client restore operation.
If processes are often canceled by other processes, consider whether you can make more drives available for ADSM use. Otherwise, review your scheduling of operations to reduce the contention for drives.
The MOUNTWAIT parameter specifies the maximum amount of time, in minutes, that the server waits for a manual (or operator controlled) volume mount request to be satisfied before canceling the request. The default mount wait period is 60 minutes; the maximum value for this parameter is 9999 minutes.
The MOUNTRETENTION parameter specifies the amount of time that a mounted volume should remain mounted after its last I/O activity. If this idle time limit is reached, the server dismounts the volume. The default mount retention period is 60 minutes; the maximum value for this parameter is 9999 minutes.
For example, if the mount retention value is 60, and a mounted volume remains idle for 60 minutes, then the server dismounts the volume.
If a volume is used frequently, you can improve performance by setting a longer mount retention period to avoid unnecessary mount and dismount operations.
If mount operations are being handled by manual, operator-assisted activities, you may want to use a large mount retention period. For example, if only one operator supports your entire operation on a weekend, then define a long mount retention period so that the operator is not being asked to mount volumes every few minutes.
While ADSM has a volume mounted, the drive is allocated to ADSM and cannot be used for anything else. If you need to free the drive for other uses, you can cancel ADSM operations that are using the drive and then dismount the volume. For example, you can cancel server migration or backup operations. For information on how to cancel processes and dismount volumes, see "Canceling Server Processes" and "Dismounting an Idle Volume".
By using the PREFIX parameter, you can specify a prefix value that is used to construct the file name string that is stored in the label area of each tape volume.
The prefix string is used as the prefix of the file name that is written to the label of each tape.
The default value for the tape label prefix string is ADSM.
You can use the FORMAT parameter to specify the recording format
used by ADSM when writing data to a tape. The following tables show the
values supported for the tape device classes:
| Device Class | Reference |
|---|---|
| 4MM | Table 5 |
| 8MM | Table 6 |
| DLT | Table 7 |
| DTF | Table 8 |
| QIC | Table 9 |
| 3570 | Table 10 |
| 3590 | Table 11 |
| CARTRIDGE | Table 12 |
| ECARTRIDGE | Table 13 |
Use the FORMAT=DRIVE parameter only if all drives that can be accessed by the device class are identical. If some drives associated with a device class support a higher density format than others, mount errors can occur when you specify FORMAT=DRIVE.
For example, suppose a device class uses two incompatible devices such as an IBM 7208-2 and an IBM 7208-12. The server might select the high-density recording format of 8500 for each of two new volumes. Later, if the two volumes are to be mounted concurrently, one fails because only one of the drives is capable of the high-density recording format.
The recording format that ADSM uses for a given tape volume is selected
when the first piece of data is written to the volume. Note that
updating the FORMAT parameter of a device class does not affect tapes that
already contain data until those tapes are rewritten from the
beginning. This process may happen after a volume is reclaimed or
deleted, or after all of the data on the volume expires.
Table 5. Recording Format and Default Estimated Capacity for 4mm Tape Volumes
| Recording Format | Estimated Capacity | Description |
|---|---|---|
| DDS1 | 1.3GB (60-meter) 2.0GB (90-meter) | Specifies that ADSM writes data using the DDS-1 recording format, without compression. The result is a cartridge capacity of 1.3GB on 60-meter tapes and 2.0GB on 90-meter tapes. This format only applies to 60- and 90-meter tapes. |
| DDS1C | 1.3GB (60-meter) 2.0GB (90-meter) | Specifies that ADSM writes data using the DDS-1 recording format, with compression enabled. The result is a cartridge capacity of approximately 1.3GB on a 60-meter tape, or 2.0GB on a 90-meter tape. However, this format uses the tape drive's hardware compression feature, and the actual capacity may be greater, depending on the effectiveness of compression. |
| DDS2 | 4.0GB | Specifies that ADSM writes data using the DDS-2 recording format, without compression. The result is a cartridge capacity of 4.0GB on 120-meter tapes. This format only applies to 120-meter tapes. |
| DDS2C | 8.0GB | Specifies that ADSM writes data using the DDS-2 recording format, with compression. The result is a cartridge capacity of 8.0GB on 120-meter tapes. However, this format uses the tape drive's hardware compression feature, and the actual capacity may be greater, depending on the effectiveness of compression. This format only applies to 120-meter tapes. |
| DDS3 | 12.0GB | Specifies that ADSM writes data using the DDS-3 recording format, without compression. The result is a cartridge capacity of 12.0GB on 125-meter tapes. This format only applies to 125-meter tapes. |
| DDS3C | 24.0GB | Specifies that ADSM writes data using the DDS-3 recording format, with compression. The result is a cartridge capacity of 24.0GB on 125-meter tapes. This format only applies to 125-meter tapes. |
| DRIVE | -- | Lets the server select the recording format to use based on the drive on which the volume is mounted. |
Table 6. Recording Format and Default Estimated Capacity for 8mm Tape Volumes
| Recording Format | Estimated Capacity | Description |
|---|---|---|
| 8200 | 2.3GB | Basic recording format for a standard 112-meter tape cartridge. |
| 8200C | 3.5GB | Specifies that ADSM writes data using the 8200C recording format for standard 112-meter tape cartridges. However, this format uses the tape drive's hardware compression feature, and the actual capacity may be greater than 3.5GB, depending on the effectiveness of the compression feature. |
| 8500 | 5.0GB | Enhanced recording format for a standard 112-meter tape cartridge. |
| 8500C | 7.0GB | Specifies that ADSM writes data using the 8500C recording format for standard 112-meter tape cartridges. However, this format uses the tape drive's hardware compression feature, and the actual capacity may be greater than 7.0GB, depending on the effectiveness of the compression feature. |
| 8900 | 20.0GB | 8900 recording format for a standard 170-meter AME tape cartridge. |
| AIT | 25.0GB | Specifies that ADSM writes data using the AIT recording format on Sony T3N. |
| AITC | 50.0GB | Specifies that ADSM writes data using the AITC recording format on Sony T3N. This format uses the tape drive's hardware compression feature, and the actual capacity may be greater than 50.0GB, depending on the effectiveness of the compression feature. |
| DRIVE | -- | Lets the server select the recording format to use based on the drive on which the volume is mounted. |
Table 7. Recording Format and Default Estimated Capacity for Digital Linear Tape Volumes
| Recording Format | Estimated Capacity | Description |
|---|---|---|
| DLT10 | 10GB | Specifies that ADSM writes data using the DLT10 recording format on CompacTape III or CompacTape IV tape cartridges. |
| DLT10C | 20GB | Specifies that ADSM writes data using the DLT10C recording format on CompacTape III or CompacTape IV tape cartridges. However, this format uses the tape drive's hardware compression feature, and the actual capacity may be greater than 20GB, depending on the effectiveness of the compression feature. |
| DLT15 | 15GB | Specifies that ADSM writes data using the DLT15 recording format on
CompacTape III XT tape cartridges.
Attention: Use this format only with CompacTape III XT cartridges in a DLT2000XT, DLT4000, or DLT7000 tape drive. |
| DLT15C | 30GB | Specifies that ADSM writes data using the DLT15C recording format on
CompacTape III XT tape cartridges. However, this format uses the tape
drive's hardware compression feature, and the actual capacity may be
greater than 30GB, depending on the effectiveness of the compression
feature.
Attention: Use this format only with CompacTape III XT cartridges in a DLT2000XT, DLT4000, or DLT7000 tape drive. |
| DLT20 | 20GB | Specifies that ADSM writes data using the DLT20 recording format on
CompacTape IV tape cartridges.
Attention: Use this format only with CompacTape IV cartridges in a DLT4000 or DLT7000 drive. |
| DLT20C | 40GB | Specifies that ADSM writes data using the DLT20C recording format on
CompacTape IV tape cartridges. However, this format uses the tape
drive's hardware compression feature, and the actual capacity may be
greater than 40GB, depending on the effectiveness of the compression
feature.
Attention: Use this format only with CompacTape IV cartridges in a DLT4000 or DLT7000 drive. |
| DLT35 | 35.0GB | Specifies that ADSM writes data using the DLT35 recording format on
CompacTape IV tape cartridges.
Attention: Use this format only with CompacTape IV cartridges in a DLT7000 drive. |
| DLT35C | 70.0GB | Specifies that ADSM writes data using the DLT35C recording format on
CompacTape IV tape cartridges.
Attention: Use this format only with CompacTape IV cartridges in a DLT7000 drive. |
| DRIVE | -- | Lets the server select the recording format to use based on the drive on which the volume is mounted. |
Table 8. Recording Format and Default Estimated Capacity for DTF Tape Volumes
| Recording Format | Estimated Capacity | Description |
|---|---|---|
| DTF | 12.0GB or 42.0GB | Specifies that ADSM writes data to a DTF drive using the DTF recording format. Two media formats are available with SONY DTF. The GW-240 stores 12.0GB of data and the GW-730L store 42.0GB of data without compression. |
| DRIVE | -- | Specifies that ADSM selects the highest format that can be supported by the sequential access drive on which a volume is mounted. Total storage capacities are based on the media used. |
Table 9. Recording Format and Default Estimated Capacity for QIC Tape Volumes
| Recording Format | Estimated Capacity | Description |
|---|---|---|
| QIC120 | 26MB-172MB | Specifies that ADSM writes data using the QIC120 recording format. |
| QIC150 | 31MB-207MB | Specifies that ADSM writes data using the QIC150 recording format. |
| QIC525 | 65MB-427MB | Specifies that ADSM writes data using the QIC525 recording format. |
| QIC1000 | 169MB-1.1GB | Specifies that ADSM writes data using the QIC1000 recording format. |
| QIC2GB | 2.5GB | Specifies that ADSM writes data using the QIC2GB recording format. |
| QIC5010 | 13.0GB | Specifies that ADSM writes data using the QIC5010 recording format. |
| QIC5010C | 26.0GB | Specifies that ADSM writes data using the QIC5010C recording format with 2:1 data compression ratio. |
| DRIVE | -- | Lets the server select the recording format to use based on the drive on which the volume is mounted. |
Table 10. Recording Format and Default Estimated Capacity for 3570 Tape Volumes
| Recording Format | Estimated Capacity | Description |
|---|---|---|
| 3570B | 5GB | Specifies that ADSM writes data using the basic (uncompressed) recording format. |
| 3570C | 5GB | Specifies that ADSM writes data using the compressed recording format. This format uses the tape drive's hardware compression feature, which may allow for greater capacity depending on the effectiveness of the compression. |
| DRIVE | -- | Lets the server select the highest recording format to be used based on the drive on which the volume is mounted. |
Table 11. Recording Format and Default Estimated Capacity for 3590 Tape Volumes
| Recording Format | Estimated Capacity | Description |
|---|---|---|
| 3590B | 10GB | Specifies that ADSM writes data using the basic (uncompressed) recording format. |
| 3590C | 10GB | Specifies that ADSM writes data using the compressed recording format. This format uses the tape drive's hardware compression feature, which may allow for greater capacity depending on the effectiveness of the compression. |
| DRIVE | -- | Lets the server select the highest recording format to be used based on the drive on which the volume is mounted. |
Table 12. Recording Format and Default Estimated Capacity for Cartridge Tape Volumes
| Recording Format | Estimated Capacity | Description |
|---|---|---|
| 3480 | 180MB | 18-track basic recording format |
| 3480XF | 180MB | 18-track compacted recording format |
| 3490B | 360MB | 36-track basic recording format |
| 3490C | 360MB | 36-track compacted recording format |
| DRIVE | -- | Lets the server select the recording format to be used based on the drive on which the volume is mounted. |
Table 13. Recording Format and Default Estimated Capacity for ECARTRIDGE Tape Volumes
| Recording Format | Estimated Capacity | Description |
|---|---|---|
| 18T | 360MB | 18-track basic recording format |
| 36T | 720MB | 36-track extended recording format |
| SD3A | 10GB | Basic recording format for a 91-meter tape cartridge |
| SD3B | 25GB | Basic recording format for a 204-meter tape cartridge |
| SD3C | 50GB | Basic recording format for a 392-meter tape cartridge |
| DRIVE | -- | Lets the server select the recording format to be used based on the drive on which the volume is mounted. |
ADSM estimates the capacity of the volumes in a storage pool based on the parameters assigned to the device class that is associated with the storage pool. The estimated capacity value is also used by ADSM when making decisions about when to initiate a reclamation process for volumes in the storage pool. For more information on how ADSM uses the estimated capacity value, see "How ADSM Fills Volumes".
You can either accept the default estimated capacity value for a given device class or explicitly specify an estimated capacity that you want the server to use instead of the default.
For tape device classes, the default values selected by the server depend
on the recording format used to write data to the volume. These values
are listed by device class in the following tables:
| Device Class | Reference |
|---|---|
| 4MM | Table 5 |
| 8MM | Table 6 |
| DLT | Table 7 |
| DTF | Table 8 |
| QIC | Table 9 |
| 3570 | Table 10 |
| 3590 | Table 11 |
| CARTRIDGE | Table 12 |
| ECARTRIDGE | Table 13 |
Before the server can mount a volume, it must know which drives can be used to satisfy the mount request. This process is done by specifying the library when the device class is defined. The library must contain drives that can be used to mount the volume.
Note that only one library can be associated with a given device class. However, multiple device classes can reference the same library. Unless you are using the DRIVES value for MOUNTLIMIT, you must ensure that the numeric value of the mount limits of all device classes do not exceed the number of drives defined in the referenced library.
There is no default value for this parameter. It is required, and so must be specified when the device class is defined.
| Note: | If the library associated with this device class is EXTERNAL type, it is recommended that you explicitly specify the mount limit instead of using MOUNTLIMIT=DRIVES. |
To use tape devices that are supported by a tape device driver, you must define a device class whose device type is GENERICTAPE. Do this by issuing a DEFINE DEVCLASS command with the parameter DEVTYPE=GENERICTAPE.
When you specify the GENERICTAPE device type for a manual library that has more than one drive defined, ensure that the device types and recording formats of the drives are compatible. Because the devices are controlled by a device driver, the ADSM server is not aware of the following:
If you have a 4mm device and an 8mm device, you must define separate manual libraries for each device.
If you have a manual library defined with two device classes of GENERICTAPE, ensure the recording formats are the same for both drives.
Other parameters specify how to manage server storage operations involving the new device class:
You can update the device class information by issuing the UPDATE DEVCLASS command.
The LIBRARY parameter for a GENERICTAPE device class is used as described in "Library".
The mount limit value for a GENERICTAPE device class is used as described in "Mount Limit".
The mount retention value for a GENERICTAPE device class is used as described in "Mount Retention Period".
You can specify an estimated capacity value of any volumes defined to a storage pool categorized by a GENERICTAPE device class.
The default ESTCAPACITY value for a volume in a GENERICTAPE device class is 1GB. Specify a capacity appropriate for your particular tape drive.
The mount wait value for a GENERICTAPE device class is used as described in "Mount Wait Period".
To use optical media, you must define a device class by issuing the DEFINE
DEVCLASS command with a DEVTYPE parameter for one of the optical
devices:
| Parameter | Description |
|---|---|
| OPTICAL | 5.25-inch rewritable optical media |
| WORM | 5.25-inch write-once optical media |
| WORM12 | 12-inch write-once optical media. Valid on AIX 4.1.4 or subsequent systems. |
| WORM14 | 14-inch write once optical media. Valid on AIX 4.1.4 or subsequent systems. |
Other parameters specify how to manage data storage operations involving the new device class:
You can update the device class information by issuing the UPDATE DEVCLASS command.
The LIBRARY parameter for OPTICAL, WORM, WORM12, and WORM14 device classes is used as described in "Library".
The mount limit value for OPTICAL, WORM, WORM12, and WORM14 device classes is used as described in "Mount Limit".
The mount wait period for OPTICAL, WORM, WORM12, and WORM14 device classes is used as described in "Mount Wait Period".
The mount retention period for OPTICAL, WORM, WORM12, and WORM14 device classes is used as described in "Mount Retention Period".
ADSM estimates the capacity of the volumes in a storage pool based on the parameters assigned to the device class that is associated with the storage pool. The estimated capacity value is used by ADSM when making decisions about when to initiate a reclamation process for volumes in the storage pool. It is also used to generate storage pool and volume reports. As a volume is written and filled, the server determines the actual capacity of the volume and uses this instead of the estimated capacity.
You can either accept the default estimated capacity value for a given device class or explicitly specify an estimated capacity that you want the server to use instead of the default.
You can use the FORMAT parameter to specify the recording format
used by ADSM when writing data to an optical cartridge. The following
values are supported for OPTICAL, WORM, WORM12, and WORM14 device classes (Table 14):
Table 14. Recording Format for OPTICAL, WORM, WORM12, and WORM14 Drives
| Recording Format | Description | ||
|---|---|---|---|
| 650MB | Used with optical cartridges whose capacity is 650MB.
| ||
| 1300MB | Used with optical cartridges whose capacity is 1300MB.
| ||
| 2600MB | Used with optical cartridges whose capacity is 2600MB.
| ||
| 5600MB | Used only with WORM12 optical cartridges whose capacity is 5600MB. | ||
| 10200MB | Used only with WORM14 optical cartridges whose capacity is 10200MB. | ||
| 12000MB | Used only with WORM12 optical cartridges whose capacity is 12000MB. | ||
| 14800MB | Used only with WORM14 optical cartridges whose capacity is 14800MB. | ||
| DRIVE | Allows the server to select the recording format to be used based on the capabilities of the drive used to access the optical disk. |
The FILE device type is used for special device classes whose storage volumes are not physical units, such as tape or optical cartridges, but simulated storage volumes. Data is written sequentially into standard files in the file system of the server machine. You can define this device class by issuing a DEFINE DEVCLASS command with the DEVTYPE=FILE parameter.
| Note: | Do not use raw partitions with a device class type of FILE. |
Because each volume in a FILE device class is actually a file, a volume name is a fully qualified file name string.
When you define the FILE device class, you can supply the following parameters to manage server storage operations for the new device class:
You can update the device class information by issuing the UPDATE DEVCLASS command.
The mount limit value for FILE device classes is used to restrict the number of mount points (volumes or files) that can be concurrently opened for access by server storage and retrieval operations. Any attempts to access more volumes than indicated by the mount limit causes the requester to wait. The default value is 1. The maximum value for this parameter is 256.
| Note: | The MOUNTLIMIT=DRIVES parameter is not valid for the FILE device class. |
When selecting a mount limit for this device class, consider how many ADSM processes you want to run at the same time.
ADSM automatically cancels some processes to run other, higher priority processes. If the server is using all available mount points in a device class to complete higher priority processes, lower priority processes must wait until a mount point becomes available. For example, ADSM cancels the process for a client backup if the mount point being used is needed for a server migration or reclamation process. ADSM cancels a reclamation process if the mount point being used is needed for a client restore operation.
Also consider the resources available on the target server when setting mount limits. Do not set a high mount limit value if the target cannot move enough data or access enough data to satisfy all of the requests.
If processes are often cancelled by other processes, consider whether you can make more mount points available for ADSM use. Otherwise, review your scheduling of operations to reduce the contention for resources.
You can specify a maximum capacity value that restricts the size of volumes (that is, files) associated with a FILE device class. Use the MAXCAPACITY parameter of the DEFINE DEVCLASS command. When the server detects that a volume has reached a size equal to the maximum capacity, it treats the volume as full and stores any new data on a different volume.
The default MAXCAPACITY value for a FILE device class is 4MB.
You can specify the directory location of the files used in the FILES device class. The default is the current working directory of the server at the time the command is issued, unless the DSMSERV_DIR environment variable is set. For more information on setting the environment variable, refer to ADSM Quick Start.
The directory name identifies the location where the server places the files that represent storage volumes for this device class. While processing the command, the server expands the specified directory name into its fully qualified form, starting from the root directory.
Later, if the server needs to allocate a scratch volume, it creates a new
file in this directory. The following lists the file name extension
created by the server for scratch volumes depending on the type of data that
is stored.
| For scratch volumes used to store this data: | The file extension is: |
|---|---|
| Client data | .BFS |
| Export | .EXP |
| Database backup | .DBB |
| Dump | .DMP |
The SERVER device type is used for special device classes whose storage volumes are not directly attached to this server. A volume with device type SERVER consists of one or more files archived in the server storage of another server, called a target server. You can define this device class by issuing a DEFINE DEVCLASS command with the DEVTYPE=SERVER parameter. For information about how to use a SERVER device class, see Chapter 4. "Storing Data on Another Server".
Other parameters specify how to manage data storage operations for the new device class:
You can update the device class information by issuing the UPDATE DEVCLASS command.
The ADSM server on which you define a SERVER device class is called a source server. The source server uses the SERVER device class to store data on another ADSM server, called a target server.
When defining a SERVER device class, specify the name of the target server. The target server must already be defined by using the DEFINE SERVER command. See Chapter 4. "Storing Data on Another Server" for more information.
Use the mount limit value for SERVER device classes to restrict the number of simultaneous sessions between the source server and the target server. Any attempts to access more sessions than indicated by the mount limit causes the requester to wait. The default mount limit value is 1. The maximum value for this parameter is 256.
| Note: | The MOUNTLIMIT=DRIVES parameter is not valid for the SERVER device class. |
When selecting a mount limit, consider your network load balancing and how many ADSM processes you want to run at the same time.
ADSM automatically cancels some processes to run other, higher priority processes. If the server is using all available sessions in a device class to complete higher priority processes, lower priority processes must wait until a session becomes available. For example, ADSM cancels the process for a client backup if a session is needed for a server migration or reclamation process. ADSM cancels a reclamation process if the session being used is needed for a client restore operation.
If processes are often cancelled by other processes, consider whether you can make more sessions available for ADSM use. Otherwise, review your scheduling of operations to reduce the contention for network resources.
You can specify a maximum capacity value that restricts the size of files that are created on the target server to store data for the source server. The default MAXCAPACITY value is 500MB. The storage pool volumes of this device type are explicitly set to full when the volume is closed and dismounted.
You can specify the amount of time, in minutes, to retain an idle sequential access volume before dismounting it. The default value is 60. The maximum value you can specify for this parameter is 9999. This parameter can improve response time for sequential access media mounts by leaving previously mounted volumes online.
You can specify a prefix that the source server will use as the beginning portion of the high-level archive file name on the target server.
You can specify a retry period for communications with the target server. When there is a communications failure, this period determines the amount of time during which the source server continues to attempt to connect to the target server.
You can specify how often the source server tries to connect to the target server when there is a communications failure. During the retry period, the source server tries to connect again as often as indicated by the retry interval.