Using Virtual Tape on the IBM System i5

Resolving The Problem

Key Advantages of Using Virtual Tape with Image Catalog

Virtual tape supports all save/restore commands and APIs (except SAVSTG). Using virtual tapes and media can be faster than saving directly to tape because it offers similar performance to saving to save files. The best performance results when the virtual tape is configured in a separate ASP or iASP.
Note: Configuring virtual tape into an IASP that is being geographically mirrored has not been tested; therefore, it could likely produce undesirable results.
Note: Virtual tape can only use a Local Image Catalog and does not work with a Remote Image Catalog

Using virtual tapes eliminates the following Save File limitations:

o	One library per save file.
o	SAVSYS not supported on save file.
o	Parallel saves not supported on save file.
o	1 TB size limitation on save file.

Using virtual tape also eliminates the following media error limitations:

o	Saves ending because of tape device or media errors.
o	Save-while-active checkpoint restriction: -- Single checkpoint for each library. -- Once the checkpoint is reached and a media error occurs, saves cannot be restarted.

Duplicate saves to media (DUPTAP or DUPMEDBRM) can occur:

o	When tape devices are available.
o	At your convenience.

On-site and off-site storage is available to:

o	Keep virtual volumes on systems, as needed.
o	Keep duplicated volumes off-site.

Considerations

The following factors must be considered before using virtual tape:

o	Additional DASD is required. If doing a full system save to virtual tape on your 100GB system, 45 percent of free DASD is required to do the save. Note: For ASPs smaller than 100GB, virtual tape will not allocate more than 95% of the ASP storage. For ASPs larger than 100GB, virtual tape will not allocate additional storage once the amount of free space reaches 5GB. When unsure if there is enough free storage to support the image size, it is recommended that *IMGSIZ be used . In summary, the lesser of 5 percent or 5GB of DASD storage remains unallocated.
o	Your system cannot be installed from a SAVSYS on virtual media D-IPL and can be done only from physical media (Tape or CD/DVD) or External Virtual Tape (ProtecTIER).
o	If using ASPs and UDFS, make sure the UDFS is mounted when the image catalog is created
o	Using virtual tape may not always be faster because: -- Tape Technology -- System Configuration and Environment
o	Data compaction is not supported on virtual media. Note: When running the DUPTAP or DUPMEDBRM command, compaction does not occur automatically. This is because the default for Data Compaction on the DUPTAP and DUPMEDBRM command is set to *FROMFILE.
o	If using Data Compression, this causes a significant performance impact . The DTACPR parameter on save commands default is *DEV or *NO. If this value is changed to *YES, SNA Low Data Compression is used.
o	Up to 256 1,000,000 MB virtual tape volumes can be stored in a single image catalog.
o	On a system or partition, there can be up to 35 virtual tape devices varied on at the same time.
o	Virtual tape volumes are stored as Integrated File System objects on the System i system.
o	When the following PTFs or their superseding PTFs are applied, the behavior of the DUPTAP command when the source device is virtual tape and COMPACT(*FROMFILE) is specified will be changed. COMPACT(*FROMFILE) would be treated the same as COMPACT(*YES) when the input device is virtual tape. COMPACT(*NO) could still be used to turn off compaction. The PTFs affecting this and DUPTAP performance at V5R4M0 are: SI24891, MF39598, MF40282, MF39601 (The reason for the change is that without compaction there is no noticeable performance improvement with the PTF, and we do not want to require the customers using virtual tape to have to change the way that they do things before they get a benefit from the PTF.)
o	When any image catalog is in a READY Status and the WRKIMGCLG command and a *LINK, SAVBRM, or SAV is run for that directory, the stream files are not saved. If the image catalog is in a Not Ready status, the image catalog entries will be saved and this could result in significant increase in the amount of data being saved. After creating virtual tape images, they are automatically included when performing a full system save using GO SAVE, Option 21. The virtual tape images could significantly increase the time it takes to complete the Option 21 save operation, even if the image catalog entries do not contain data. To exclude the virtual images from a full system save, use one of the following strategies: -- Use the Change Attribute (CHGATR) command to mark the image catalog directory as non-saveable. For example: CHGATR OBJ('/Catalog-Path') ATR(*ALWSAV) VALUE(*NO) -- Use the Load Image Catalog (LODIMGCLG) command to make the image catalog ready. Image catalogs with a ready status are omitted from the save. In an attended save, omitting the image catalog directories can be specified on the Save Object (SAV) command.
o	The initialize Tape (INZTAP) command makes any pre-existing data on the virtual tape volume inaccessible by the virtual tape device. Running the INZTAP command and specifying CLEAR(*YES) can be used to delete any existing data in a virtual tape volume; however, this should be used only if there are security concerns with the existing data because this operation can take a long time and uses significant system resources.
o	It is recommended that PTF MF41110 (V5R4) be loaded and applied before using Virtual tape. More information can be found in APAR MA34516.

Using Virtual Tape from Other Partitions or iSCSI Attached Servers

The host partition must mount the virtual tape volume before it can be used by another partition. or iSCSI attached sever.

(This is for Linux guest partitions and is not supported on AIX Guest partitions or on i5 client hosted partitions.)

To use virtual tape from other partitions, do the following:

1.	Ensure that the virtual tape device description has the unload device at vary off parameter set to the value *NO.
2. 3.	Mount the virtual volume in the virtual tape device using the image catalog commands. Make sure that the virtual volume density is *VRT256K
4.	Vary off the virtual tape device. Note: The virtual volume is still mounted.

The other partition or the iSCSI-attached server can now use the previously mounted virtual tape volume through virtual I/O to the virtual tape device. Only the mounted volume can be used. Volume spanning is not supported.

The virtual tape device is configured as a 3580 model 002 tape device to the other partitions or iSCSI-attached servers.

Note: The image catalog commands should not be used to remove or change the virtual tape volumes while they are being used by other partitions or iSCSi-attached servers. Only the host operating system partition can unload (eject) the mounted volume.

Density

The density (format) parameter limits the block size that can be written to a virtual tape volume so that the volume will be compatible for duplication to your physical tape device.

o	Volumes with a density of *VRT256K use an optimum block size of 256KB and are compatible with 35xx type devices and the newer QIC tape devices.
o	Volumes with a density of *VRT240K use an optimum block size of 240KB and are compatible with VXA and 8mm technology devices and the 35xx and newer QIC devices.
o	Volumes with a density of *VRT64K use an optimum block size of 64KB and are compatible with 3490F Model 18 track media, VXA and 8mm technology devices, and with the 35xx and newer QIC devices.
o	Volumes with a density of *VRT32K do not use an optimum block size and are compatible with all devices.

The virtual tape media cannot be copied to physical media if you choose an incompatible block size. Ensure a virtual tape density with a block size that is compatible with the physical tape devices on your system is selected by performing one of the following:

o	In iSeries Navigator, expand Configuration and Service > Hardware > Tape Devices > Tape Libraries > Tape Resources for tape library devices. Next, right click on the device that you want to view and select Properties to display the supported block sizes for your tape device.
o	In iSeries Navigator, expand Configuration and Service > Hardware > Tape Devices > Stand-Alone Devices for stand alone tape devices. Next, right click on the device that you want to view and select Properties to display the supported block sizes for your tape device.
o	Save a small library to your physical tape drive with the USEOPTBLK parameter set to *YES. Type DSPTAP DATA(*LABELS) in the command line, and use the Block Length field to see the block size that was used.

BRMS

BRMS does not support the following:

o	Dependent catalogs.
o	Automatic creation of volumes because the volume must be enrolled in the BRMS inventory before it can be used; Message CPF3742 will be posted and the job will end.

Consider the following when using virtual media in BRMS:

o	A Create Virtual Tape Devices Outside of BRMS must be created using the CRTDEVTAP command.
o	An Image Catalog and Virtual Volumes Outside of BRMS must be created using the following commands: CRTIMGCLG ADDIMGCLGE Use the iSeries Navigator GUI interface.
o	BRMS virtual tape acts similar to a physical tape device.
o	BRMS automatically performs virtual tape mounts.
o	If BRMS runs out of virtual volumes, the save will end. Even though virtual tape as the ability to add new virtual volumes, BRMS does not know about these as only volumes enrolled in the BRMS data base can be used

Disaster Recovery

For disaster recovery, do the following:

1.	You will need to duplicate virtual tape images to Physical Media (DUPMEDBRM) . When this is done, the physical tapes become the original saved volume and the virtual volume becomes the duplicate saved volume.
2.	To make recovery faster and easier and parallel saves are going to be used, it is advised that you keep virtual tape size such that it will fit to one physical tape,so you would get a one to one relationship when a DUPMEDBRM is run.
3.	If you used parallel saves,and then need to recover from physical media, and do not have the same amount of drives used during the save, a lot of tape changing will need to be done.
4.	Virtual Media Volumes cannot normally be shared in BRMS Network. However, it is possible using iASPs to share the volumes if the iASP is switched from one system to the other.
5.	Your system cannot be installed from a SAVSYS on virtual media D-IPL and can be done only from physical media (Tape or CD/DVD) or External Virtual Tape (ProtecTIER).

Messages Related to Virtual Tape and Media

CPF415B	Device list not correct.
CPF41B0	Incorrect image catalog name specified.
CPF41B3	No more volumes to mount from catalog. You specified VOL(*MOUNTED) and the last accessible virtual tape volume in the catalog was already used and unloaded.
CPF41B4	Virtual tape volume not available. The specified volume is in unloaded status.
CPF41B5	Virtual tape volume not found.
CPF6760	Device &1 is not ready. This error will be reported when the requested virtual volume could not be mounted. Typically this error occurs when the requested virtual volume is already mounted in a different virtual device using a reference or a dependent image catalog and the mount is not allowed.
CPF67F5	Duplicate cartridge or virtual volume name found.
CPF4373	End of Media on Device. This message is sent when the storage threshold of the ASP containing the virtual tape volume exceeds the maximum allowed storage for virtual tape, or when the maximum storage allowed threshold of the user profile that owns the virtual tape is exceeded and additional storage cannot be allocated to continue the output operation. The maximum allowed storage for virtual tape is the greater of - 95% or 5GB of free space remaining in the ASP.
CPF5386	End of media on device &25. When the allocated size of the virtual tape volume grows large enough to cause the "Maximum storage allowed" threshold for the owning user profile to be exceeded, the job will now fail with an end of media error message CPF5386. (Refer to MA31528 for more information.)
CPF4371	Device Not Operational. This message is sent when an unexpected error occurs. Possible causes are as follows: - The virtual volume stream file was removed while in use. - A force vary off was performed on an IASP containing a virtual tape volume that was in use. It will be necessary to vary the virtual tape device description off and back on with RESET(*YES) to clear the error.

Diagnostic Messages Related to Virtual Tape and Media

CPDBC04

Error on command &3 during virtual tape function &2. Reason code 26. Reason code 26 is sent when a command to mount or change a virtual volume could not be processed because the volume is currently mounted in a device. The volume will need to be unloaded or unmounted from the device it is currently in before the command can be completed.

Note: If the virtual volume was used by another partition and left mounted, there may not be any image catalogs that show that the volume is in mounted status. The CHKTAP command with ENDOPT(*UNLOAD) can be used to unload the virtual tape volume.

Reference - IBM Redbooks: Virtual Tape, SG24-7164