4.1 Command Overview

Dynamic Tape Accelerator has three options that are accessed using the CONTROL command procedure:

$ @TTI_DTA:CONTROL PREACCEL device_name tape_capacity $ @TTI_DTA:CONTROL ACCEL device_name tape_capacity $ @TTI_DTA:CONTROL DEACCEL device_name

Where device_name is the name of a tape device.

Where tape_capacity is the tape capacity in megabytes (e.g., 160).

You can also enter the following:

$ @TTI_DTA:CONTROL

DTA will then prompt you for the additional parameters required.

Valid DTA procedures are: ACCEL, PREACCEL, DEACCEL DTA procedure? Tape device to accelerate? Tape capacity in MB?

From time to time you may want to monitor tape devices without accelerating them. To do this, you can use the PREACCEL option of the CONTROL procedure. This allows you to monitor the tape device using the DTA MONITOR procedure included in this package, without altering the drive's performance.

For example, if on MSA0: you have a tape with a capacity of 160MB, to pre-accelerate you would type the following:

$ @TTI_DTA:CONTROL PREACCEL MSA0: 160

All tape write operations for MSA0: will now be pre-accelerated until you use the ACCEL option to accelerate or the DEACCEL option to deaccelerate. Tape operations to MSA0: can now be monitored using the DTA MONITOR procedure.

4.3 Accelerating a Device

$ @TTI_DTA:CONTROL ACCEL device_name tape_capacity

Tape devices can be accelerated ONLY when the tape is:

• not yet mounted
• fully rewound
• at BOT (beginning of tape)

There is no limit to the types of tape devices or number of tape devices that can be accelerated.

If you have more than one tape device that you want to accelerate, you must use the ACCEL option for each device.

For each device being accelerated, add the ACCEL command line above to your system startup command file. This will cause the tape devices specified to be accelerated each time the system is booted.

For example, if on MSA0: you have a tape with a capacity of 160MB, to accelerate you would type the following:

$ @TTI_DTA:CONTROL ACCEL MSA0: 160

All tape write operations for MSA0: will now be accelerated until you use the DEACCEL option.

4.3.1 Capacities for Special Devices

Table 4-1 Capacity in MB for Special Devices

Device Name	Capacity
TK50	95
TK70	296
TA90	200
TF85	2500
TF86	5900
Exabyte 8500 8mm	5000
Other 8mm devices	2100
4mm device	1250

Table 4-2 Capacity in MB for 9-Track Tape Devices

Reel Length	1600 BPI	6250 BPI
200	3	13
600	10	40
2400	40	160

If your tape device and capacity are not listed in the above tables, you can enter your capacity in megabytes. For example, if your tape capacity is 4 gigabytes, you would set the capacity to 4000 megabytes.

If you have a device that runs compression, you should lower the tape capacity. For example, if your tape device records 8 gigabytes in compression, you should set your capacity to 7500 megabytes.

4.4 Deaccelerating a Device

To deaccelerate device MSA0:, type the following:

$ @TTI_DTA:CONTROL DEACCEL MSA0:

All tape write operations for MSA0: will now be back to normal until you once again ACCEL the tape device.

5.1 Command Overview

Data compression effectiveness varies, depending on the data being compressed. However, use the same tape capacity in the ACCEL command whether or not you use the data compression option.

5.2 Enabling Data Compression

$ @TTI_DTA:CONTROL ACCEL device_name tape_capacity COMPRESS

Where device_name is the name of a tape device.

Where tape_capacity is the tape capacity in megabytes (e.g. 160).

Remember, tape devices can be accelerated ONLY when the tape is:

• not yet mounted
• fully rewound
• at BOT (beginning of tape)

All tape write operations will now be accelerated and compressed, until you use the DEACCEL option or re-execute the ACCEL option without the COMPRESS qualifier.

5.3 Reading Compressed Tapes

If DTA data compression is off, and you are trying to read a compressed tape, you will get an error when the tape is trying to mount. The tape will not have a valid label. Simply accelerate the tape device with the following command:

$ @TTI_DTA:CONTROL ACCEL device_name tape_capacity COMPRESS

After accelerating the drive with COMPRESS, the MOUNT will complete successfully.

5.4 Turning Data Compression Off

$ @TTI_DTA:CONTROL ACCEL device_name tape_capacity $ @TTI_DTA:CONTROL DEACCEL device_name

5.4.1 Using ACCEL to Turn Off Data Compression

To turn the data compression feature off but leave the tape drive accelerated, type the following:

$ @TTI_DTA:CONTROL ACCEL device_name tape_capacity

All tape write operations for the tape device will now be accelerated but not compressed.

5.4.2 Using DEACCEL to Turn Off Data Compression

To deaccelerate the tape device, type the following:

$@TTI_DTA:CONTROL DEACCEL device_name

All tape write operations for the tape device will now be back to normal, until you once again ACCEL the tape device.

The MONITOR procedure allows you to monitor a tape device's activity when the tape device has been either pre-accelerated or accelerated.

When the PREACCEL command is executed, the MONITOR procedure shows the non-accelerated data transfer rate to tape. When the ACCEL command is executed, the monitor shows the DTA accelerated data transfer rate.

To execute the MONITOR procedure, enter the following:

$ @TTI_DTA:MONITOR device

where device is the name of the device to be monitored.

The DTA monitor will be displayed on the screen and can be executed at any time during the backup.

• To EXIT the monitor, type CTRL/Z.
• To REFRESH the screen, type CTRL/W.

To write the monitor to a file, execute the following command after pre-accelerating or accelerating the device to be monitored:

$ @TTI_DTA:MONITOR device file_spec

where device is the name of the device to be monitored and file_spec is the location you would like to log monitor information.

You may begin recording the monitor at any time, but you only log the monitor information from that point on.

If you want to record the monitor as part of a batch job, add the following command to your batch command file:

$ SPAWN/NOWAIT @TTI_DTA:MONITOR device file_spec

where device and file_spec are as above.

6.3 The Monitor Display

Example 6-1 DTA MONITOR Sample Display

(1) DTA MONITOR (4.0) of MSA0: on 12-JAN-1997 19:13:05.14 Sample 3 User OPER, image BACKUP SYS$SYSDEVICE:[TEST]MYFILE.LIS;12 20 40 60 80 100 + - - - + - - - + - - - + - - - + - - - + (2) Percent of capacity 2|X (3) Cachesize/100KB 8|XXXX 500| 450| 400| (4) Throughput History 350| in KB/sec 300| 250| 200| X X (5) Average KB/sec: 180 150| X X X 100| X X X 50| X X X + - - - - - - - - - - - - - - - - - - - - (6) (7) (8) I/O queue len : 96 Elapsed : 12:53 Volume/Saveset: BACK02 I/O requests : 145 Func time: 0:02 Current Funct : WRITE Virtual KB/sec: 68 Est EOT : 8:13 DTA state : CACHING PHY/ACT KB/sec: 86/89 Errors : 13 Device state : OPEN PHY/ACT MB : 14/15 HW cache : NO Compression : ON

Key to DTA MONITOR Sample Display

1. The heading includes the DTA version being used, and the current date and time. Also included are the number of samples that have occurred since the monitor was started, as well as the username and the application using the tape device. If the tape device is reading or writing an ANSI labeled tape or a OpenVMS BACKUP saveset, the name of the current file being processed is also displayed.
2. The percent of tape used on the reel.
3. The cached bytes of data in 100KB increments.
4. A graphic history of data transfer rates in KB/sec increments.
5. The average KB/sec.
   Appendix E, Maximum Data Transfer Rates for Tape Devices, lists the maximum tape transfer speeds for various tape devices.
6. The first column contains:
   • I/O queue len: the number of requests on the tape device I/O queue.
   • I/O requests: the total number of I/O requests for this reel.
   • Virtual KB/sec: the virtual KBs written per second as perceived by the application.
   • PHY/ACT KB/sec: the KB/sec physically being written to the tape over the KB/sec actually being sent to the tape. The PHY KB/sec and the ACT KB/sec are always the same when compression is OFF. When compression is ON, the KB/sec being written (PHY) can be smaller; the difference being the amount that is compressed.
   • PHY/ACT MB: the MB physically written to the tape over MB that have actually been sent to the tape. The PHY MB and the ACT MB are always the same when compression is OFF. When compression is ON, the MB written (PHY) can be smaller; the difference being the amount that was compressed.
7. The second column contains:
   • Elapsed: the time elapsed since the tape was first written to
   • Func time: the time elapsed since the I/O function was last requested
   • EST EOT: the estimated time until the current volume reaches the end-of-tape marker (in minutes and seconds) as calculated by DTA
   • Errors: the number of tape errors for this reel
   • HW cache: whether the device supports hardware data caching or not (YES or NO)
8. The third column contains:
   • Volume/Saveset: the name of the current tape volume being written to.
   • Current Funct: the current tape I/O function.
   • DTA state: the DTA caching state. The state is:

     -empty-	cache is empty
     - full -	cache is full
     NEAREND	caching stopped because of near end of tape
     CACHING	will take more cache if something comes
     - pre -	the drive is pre-accelerated
     DOWN	transition period from deaccell to accell while still writing to the tape
     PAGE LIM	cannot cache anymore, memory is used up
     I/O LIM	reached I/O limit

   • Device state: the device state. The state is ALLOCATED when the tape device has been allocated, AVAILABLE when there is no activity occurring on the tape device, MOUNTED when the tape device has been mounted, OPEN when the tape device is in use, and FULL when DTA's cache is full.
   • Compression: the DTA compression state (ON or OFF).

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