The following describes tape drive attributes you can adjust to meet the needs of your system. The attributes can be displayed or changed using the Web-based System Manager Devices application, SMIT, or commands (in particular, the lsattr and the chdev commands).
Each type of tape drive only uses a subset of all the attributes.
The block size attribute indicates the block size to use when reading or writing the tape. Data is written to tape in blocks of data, with inter-record gaps between blocks. Larger records are useful when writing to unformatted tape, because the number of inter-record gaps is reduced across the tape, allowing more data to be written. A value of 0 indicates variable length blocks. The allowable values and default values vary depending on the tape drive.
Setting the Device Buffers attribute (for chdev, the mode attribute) to the yes value indicates an application is notified of write completion after the data has been transferred to the data buffer of the tape drive, but not necessarily after the data is actually written to the tape. If you specify the no value, an application is notified of write completion only after the data is actually written to the tape. Streaming mode cannot be maintained for reading or writing if this attribute is set to the no value. The default value is yes.
With the no value, the tape drive is slower but has more complete data in the event of a power outage or system failure and allows better handling of end-of-media conditions.
Setting the Extended File Marks attribute (for chdev, the extfm attribute) to the no value writes a regular file mark to tape whenever a file mark is written. Setting this attribute to the yes value writes an extended file mark. For tape drives, this attribute can be set on. The default value is no. For example, extended filemarks on 8mm tape drives use 2.2MB of tape and can take up to 8.5 seconds to write. Regular file marks use 184K and take approximately 1.5 seconds to write.
When you use an 8mm tape in append mode, use extended file marks for better positioning after reverse operations at file marks. This reduces errors.
Setting the Retension attribute (for chdev, the ret attribute) to yes instructs the tape drive to retension a tape automatically whenever a tape is inserted or the drive is reset. Retensioning a tape means to wind to the end of the tape and then rewind to the beginning of the tape to even the tension throughout the tape. Retensioning the tape can reduce errors, but this action can take several minutes. If you specify the no value, the tape drive does not automatically retension the tape. The default value is yes.
Density Setting #1 (for chdev, the density_set_1 attribute) sets the density value that the tape drive writes when using special files /dev/rmt*, /dev/rmt*.1, /dev/rmt*.2, and /dev/rmt*.3. Density Setting #2 (for chdev, the density_set_2 attribute) sets the density value that the tape drive writes when using special files /dev/rmt*.4, /dev/rmt*.5, /dev/rmt*.6, and /dev/rmt*.7. See "Special Files for Tape Drives" for more information.
The density settings are represented as decimal numbers in the range 0 to 255. A zero (0) setting selects the default density for the tape drive, which is usually the drive's high density setting. Specific permitted values and their meanings vary with different types of tape drives. These attributes do not affect the tape drive's ability to read tapes written in all densities supported by the tape drive. It is customary to set Density Setting #1 to the highest density possible on the tape drive and Density Setting #2 to the second highest density possible on the tape drive.
For tape drives that use the Reserve attribute (for chdev, the res_support attribute), specifying the yes value causes the tape drive to be reserved on the SCSI bus while it is open. If more than one SCSI adapter shares the tape device, this ensures access by a single adapter while the device is open. Some SCSI tape drives do not support reserve/release commands. Some SCSI tape drives have a predefined value for this attribute so that reserve/release commands are always supported.
The Variable Length Block Size attribute (for chdev, the var_block_size attribute) specifies the block size required by the tape drive when writing variable length records. Some SCSI tape drives require that a nonzero block size be specified in their Mode Select data even when writing variable length records. The Block Size attribute is set to 0 to indicate variable length records. Refer to the specific tape drive SCSI specification to determine whether this is required.
Setting the Data Compression attribute (for chdev, the compress attribute) to yes causes the tape drive to be in compress mode, if the drive is capable of compressing data. If so, then the drive writes data to the tape in compressed format so that more data fits on a single tape. Setting this attribute to no forces the tape drive to write in native mode (noncompressed). Read operations are not affected by the setting of this attribute. The default setting is yes.
Setting the Autoloader attribute (for chdev, the autoload attribute) to yes causes Autoloader to be active, if the drive is so equipped. If so, and another tape is available in the loader, any read or write operation that advances the tape to the end is automatically continued on the next tape. Tape drive commands that are restricted to a single tape cartridge are unaffected. The default setting is yes.
The Retry Delay attribute sets the number of seconds that the system waits after a command has failed before reissuing the command. The system may reissue a failed command up to four times. This attribute applies only to type ost tape drives. The default setting is 45.
The Read/Write Timeout or Maximum Delay for a READ/WRITE attribute sets the maximum number of seconds that the system allows for a read or write command to complete. This attribute applies only to type ost tape drives. The default setting is 144.
The Return Error on Tape Change or Reset attribute, when set, will cause an error to be returned on open when the tape drive has been reset or the tape has been changed. A previous operation to the tape drive must have taken place that left the tape positioned beyond beginning of tape upon closing. The error returned is a -1 and errno is set to EIO. Once presented to the application, the error condition is cleared. Also, reconfiguring the tape drive itself will clear the error condition.
The default value is 1024.
The general information for this attribute applies to this tape drive type.
If a tape drive is configured as a 2.0GB 4mm tape drive, the Retension, Reserve Support, Variable Length Block Size, Density Setting #1, and Density Setting #2 attributes have predefined values that cannot be changed. The density settings are predefined because the tape drive always writes in 2.0GB mode.
The default value is 1024.
The general information for this attribute applies to this tape drive type.
The user cannot change the density setting of this drive; the device reconfigures itself automatically depending on the Digital Data Storage (DDS) media type installed, as follows:
| Media Type | Device Configuration |
|---|---|
| DDS | Read-only. |
| DDS |||| | Read/write in 2.0GB mode only. |
| DDS2 | Read in either density; write in 4.0GB mode only. |
| non-DDS | Not supported; cartridge will eject. |
The general information for this attribute applies to this tape drive type.
If a tape drive is configured as a 4.0GB 4mm tape drive, the Retension, Reserve Support, Variable Length Block Size, Density Setting #1, and Density Setting #2 attributes have predefined values that cannot be changed.
The default value is 1024. A smaller value reduces the amount of data stored on a tape.
The general information for this attribute applies to this tape drive type.
The general information for this attribute applies to this tape drive type.
If a tape drive is configured as a 2.3GB 8mm tape drive, the Retension, Reserve Support, Variable Length Block Size, Data Compression, Density Setting #1, and Density Setting #2 attributes have predefined values which cannot be changed. The density settings are predefined because the tape drive always writes in 2.3GB mode.
The default value is 1024. If a tape is being written in 2.3GB mode, a smaller value reduces the amount of data stored on a tape.
The general information for this attribute applies to this tape drive type.
The general information for this attribute applies to this tape drive type.
The following settings apply:
| Setting | Meaning |
|---|---|
| 140 | 5GB mode (compression capable) |
| 21 | 5GB mode noncompressed tape |
| 20 | 2.3GB mode |
| 0 | Default (5.0GB mode) |
The default values are 140 for Density Setting #1, and 20 for Density Setting #2. A value of 21 for Density Setting #1 or #2 permits the user to read or write a noncompressed tape in 5GB mode.
The general information for this attribute applies to this tape drive type.
If a tape drive is configured as a 5.0GB 8mm tape drive, the Retension, Reserve Support, and Variable Length Block Size attributes have predefined values which cannot be changed.
The default value is 1024.
The general information for this attribute applies to this tape drive type.
The general information for this attribute applies to this tape drive type.
The drive can read and write data cartridges in 20.0GB format. During a Read command, the drive automatically determines which format is written on tape. During a Write, the Density Setting determines which data format is written to tape.
The following settings apply:
| Setting | Meaning |
|---|---|
| 39 | 20GB mode (compression capable) |
| 0 | Default (20.0GB mode) |
The default value is 39 for Density Setting #1 and Density Setting #2.
The general information for this attribute applies to this tape drive type.
If a tape drive is configured as a 20.0GB 8mm tape drive, the Retension, Reserve Support, and Variable Length Block Size attributes have predefined values which cannot be changed.
The IBM 7205 Model 311 throughput is sensitive to blocksize. The minimum recommended blocksize for this drive is 32K Bytes. Any block size less than 32K Bytes restricts the data rate (backup/restore time). The following table lists recommended block sizes by AIX command:
| AIX Command Supported | Default Block Size (Bytes) | RECOMMENDATION |
|---|---|---|
| BACKUP | 32K or 51.2K (default) | Uses either 32K or 51.2 K depending on if "Backup" is by name or not. No change is required. |
| TAR | 10K | There is an error in the manual that states a 512K byte block size. Set the Blocking Parameter to -N64. |
| MKSYSB | See BACKUP | MKSYSB uses the BACKUP Command. No change is required. |
| DD | n/a | Set the Blocking Parameter to bs=32K. |
| CPIO | n/a | Set the Blocking Parameter to -C64. |
Note: You should be aware of the capacity and throughput when you select a blocksize. Small blocksizes have a significant impact on performance and a minimal impact on capacity. The capacities of the 2.6GB format (density) and 6.0GB format (density) are significantly impacted when you use smaller than the recommended blocksizes. As an example: using a blocksize of 1024 bytes to backup 32GB of data takes approximately 22 hours. Backing up the same 32GB of data using a blocksize of 32K Bytes takes approximately 2 hours.
The general information for this attribute applies to this tape drive type.
The general information for this attribute applies to this tape drive type.
The following chart shows the Supported Data Cartridge type and Density Settings (in decimal and hex) for the IBM 7205-311 Tape Drive. When you perform a Restore (Read) Operation, the tape drive automatically sets the density to match the written density. When you perform a Backup Operation (Write), you must set the Density Setting to match the Data Cartridge that you are using.
| Supported Data Cartridges | Native Capacity | Compressed Data Capacity | Web-based System Manager or SMIT Density Setting | HEX Density Setting |
|---|---|---|---|---|
| DLTtape III | 2.6GB | 2.6GB (No Compression) | 23 | 17h |
| 6.0GB | 6.0GB (No Compression) | 24 | 18h | |
| 10.0GB | 20.0GB (Default for drive) | 25 | 19h | |
| DLTtapeIIIxt | 15.0GB | 30.6GB (Default for drive) | 25 | 19h |
| DLTtapeIV | 20.0GB | 40.0GB | 26 | 1Ah |
| 35.0GB | 70.0GB (Default for drive) | 27 | 1Bh |
Note: If you request an unsupported Native Capacity for the Data Cartridge, the drive defaults to the highest supported capacity for the Data Cartridge that is loaded into the drive.
The actual compression depends on the type of data being that is being written. (see above table) A Compression Ratio of 2:1 is assumed for this Compressed Data Capacity.
The general information for this attribute applies to this tape drive type.
The default block size is 512. The only other valid block size is 0 for variable length blocks.
The general information for this attribute applies to this tape drive type.
Writing to a 1/4-inch tape can only occur at the beginning of tape (BOT) or after blank tape is detected. If data exists on the tape, you cannot overwrite the data except at BOT. If you wish to add data to a tape that has been written and then rewound, you must space forward until the next file mark is detected, which causes the system to return an error. Only then can you start writing again.
The general information for this attribute applies to this tape drive type.
The following settings apply:
| Setting | Meaning |
|---|---|
| 16 | QIC-150 |
| 15 | QIC-120 |
| 0 | Default (QIC-150), or whatever was the last density setting by a using system. |
The default values are 16 for Density Setting #1, and 15 for Density Setting #2.
If a tape drive is configured as a 150MB 1/4-inch tape drive, the Extended File Marks, Reserve Support, Variable Length Block Size, and Data Compression attributes have predefined values which cannot be changed.
The default block size is 512. The other valid block sizes are 0 for variable length blocks, and 1024.
The general information for this attribute applies to this tape drive type.
Writing to a 1/4-inch tape can only occur at the beginning of tape (BOT) or after blank tape is detected. If data exists on the tape, you cannot overwrite the data except at BOT. If you want to add data to a tape that has been written and then rewound, you must space forward until the next file mark is detected, which causes the system to return an error. Only then can you start writing again.
The general information for this attribute applies to this tape drive type.
The following settings apply:
| Setting | Meaning |
|---|---|
| 17 | QIC-525* |
| 16 | QIC-150 |
| 15 | QIC-120 |
| 0 | Default (QIC-525), or whatever was the last density setting by a using system. |
* QIC-525 is the only mode that supports the 1024 block size.
The default values are 17 for Density Setting #1, and 16 for Density Setting #2.
If a tape drive is configured as a 525MB 1/4-inch tape drive, the Extended File Marks, Reserve Support, Variable Length Block Size, and Data Compression attributes have predefined values which cannot be changed.
The default block size is 512. The other valid block sizes are 0 for variable length blocks, and 1024.
The general information for this attribute applies to this tape drive type.
Writing to a 1/4-inch tape can only occur at the beginning of tape (BOT) or after blank tape is detected. If data exists on the tape, you cannot overwrite the data except at BOT. If you wish to add data to a tape that has been written and then rewound, you must space forward until the next file mark is detected, which causes the system to return an error. Only then can you start writing again.
The general information for this attribute applies to this tape drive type.
The following settings apply:
| Setting | Meaning |
|---|---|
| 21 | QIC-1000* |
| 17 | QIC-525* |
| 16 | QIC-150 |
| 15 | QIC-120 |
| 0 | Default (QIC-1000), or whatever was the last density setting by a using system. |
* QIC-525 and QIC-1000 are the only modes that support the 1024 block size.
The default values are 21 for Density Setting #1, and 17 for Density Setting #2.
If a tape drive is configured as a 1200MB 1/4-inch tape drive, the Extended File Marks, Reserve Support, Variable Length Block Size, and Data Compression attributes have predefined values which cannot be changed.
The IBM 12000MB 4mm Tape Drive's throughput is sensitive to blocksize. The minimum recommended blocksize for this drive is 32K Bytes. Any block size less than 32K Bytes restricts the data rate (backup/restore time). The following table lists recommended block sizes by AIX command:
| AIX Command Supported | Default Block Size (Bytes) | RECOMMENDATION |
|---|---|---|
| BACKUP | 32K or 51.2K (default) | Will use either 32K or 51.2 K depending on if "Backup" is by name or not. No change is required. |
| TAR | 10K | There is an error in the manual that states a 512K byte block size. Set the Blocking Parameter to -N64. |
| MKSYSB | See BACKUP | MKSYSB uses the BACKUP Command. No change is required. |
| DD | n/a | Set the Blocking Parameter to bs=32K. |
| CPIO | n/a | Set the Blocking Parameter to -C64. |
Note: You should be aware of the capacity and throughput when you select a blocksize. Small blocksizes have a significant impact on performance and a minimal impact on capacity.
The general information for this attribute applies to this tape drive type.
The general information for this attribute applies to this tape drive type.
The following chart shows the Supported Data Cartridge type and Density Settings (in decimal and hex) for the IBM 12000MB 4mm Tape Drive. When you perform a Restore (Read) Operation, the tape drive automatically sets the density to match the written density. When you perform a Backup Operation (Write), you must set the Density Setting to match the Data Cartridge you are using.
| Supported Data Cartridges | Native Capacity | Compressed Data Capacity | Web-based System Manager or SMIT Density Setting | HEX Density Setting |
|---|---|---|---|---|
| DDS III | 2.0GB | 4.0GB | 19 | 13h |
| DDS2 | 4.0GB | 8.0GB | 36 | 24h |
| DDS3 | 12.0GB | 24.0GB | 37 | 25h |
Note: If you request an unsupported Native Capacity for the Data Cartridge, the drive defaults to the highest supported capacity for the Data Cartridge that is loaded into the drive.
The actual compression depends on the type of data being that is being written. (see above table) A Compression Ratio of 2:1 is assumed for this Compressed Data Capacity.
The general information for this attribute applies to this tape drive type.
The default block size is 512. The other valid block sizes are 0 for variable length blocks, and 1024.
The general information for this attribute applies to this tape drive type.
Writing to a 1/4-inch tape can only occur at the beginning of tape (BOT) or after blank tape is detected. If data exists on the tape, you cannot overwrite the data except at BOT. If you wish to add data to a tape that has been written and then rewound, you must space forward until the next file mark is detected, which causes the system to return an error. Only then can you start writing again.
The general information for this attribute applies to this tape drive type.
| Setting | Meaning |
|---|---|
| 33 | QIC-5010-DC* |
| 34 | QIC-2GB* |
| 21 | QIC-1000* |
| 17 | QIC-525* |
| 16 | QIC-150 |
| 15 | QIC-120 |
| 0 | Default (QIC-5010-DC)* |
* QIC-525, QIC-1000, QIC-5010-DC, and QIC-2GB are the only modes that support the 1024 block size.
The default values are 33 for Density Setting #1, and 34 for Density Setting #2.
If a tape drive is configured as a 13000MB 1/4-inch tape drive, the Extended File Marks, Reserve Support, and Variable Length Block Size attributes have predefined values which cannot be changed.
The default block size is 1024.
The general information for this attribute applies to this tape drive type.
| Setting | Meaning |
|---|---|
| 3 | 6250 bits per inch (bpi) |
| 2 | 1600 bpi |
| 0 | Whichever writing density was used previously. |
The default values are 3 for Density Setting #1, and 2 for Density Setting #2.
If a tape drive is configured as a 1/2-inch 9-track tape drive, the Extended File Marks, Retension, Reserve Support, Variable Length Block Size, and Data Compression attributes have predefined values which cannot be changed.
The default block size is 1024. This drive features a high data transfer rate, and block size can be critical to efficient operation. Larger block sizes can greatly improve operational speeds, and in general, the largest possible block size should be used.
Note: Increasing the block value can cause incompatibilities with other programs on your system. If this occurs, you receive the following error message while running those programs:
A system call received a parameter that is not valid.
The general information for this attribute applies to this tape drive type.
The general information for this attribute applies to this tape drive type.
This drive features a tape sequencer, an autoloader that sequentially loads and ejects a series of tape cartridges from the cartridge loader. For this function to operate properly, the front panel switch should be in the AUTO position and the Autoloader attribute must be set to yes.
The system default is 512, but this should be adjusted to the default block size for your tape drive. Typical values are 512 and 1024. 8mm and 4mm tape drives usually use 1024 and waste space on the tape if the block size attribute is left at 512. 0 indicates variable block size on some drives.
The general information for this attribute applies to this tape drive type.
The general information for this attribute applies to this tape drive type.
The default value is 0 for both of these settings. Other values and their meanings vary for different tape drives.
The default value is no. This may be set to yes, if the drive supports reserve/release commands. If you are unsure, no is a safer value.
0 is the default value. Nonzero values are used primarily on quarter inch cartridge (QIC) drives. Refer to the SCSI specification for the particular tape drive for advice.
This attribute applies exclusively to type ost tape drives
This attribute applies exclusively to type ost tape drives
If a tape drive is configured as an Other SCSI tape drive, the Extended File Marks, Retension, and Data Compression attributes have predefined values which cannot be changed.