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Poor performance on DLT Drive !

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Asim_5
Frequent Advisor

Poor performance on DLT Drive !

HI

We are having slow performance issue on DLT Tape drive (DS-TZ90N-VW) which is connected with GS80 server. The backup on DAT tape takes 3 hours and the same backup take 2 hours and 30 min. on DLT Tape. According to the specs of DLT is should be finished in 30 min. The size of data is 24 GB. The specs of DLT says that its speed is 46 GB/ Hour.

Can anyone guide me where the problem is?

Regards

Asim

13 REPLIES
Dave Dewar
Trusted Contributor

Re: Poor performance on DLT Drive !

Hi Asim,

The fact you are getting similar performance on the DAT and DLT drive sugegsts you are experiencing system performance bottlenecks rather than drive bottlenecks. You don't mention what DAT or DLT drive you have or any details on your system/disk config etc etc so it is difficult to comment further.

We have provided a couple of good performance trouble shooting guides that should help you, links below, this makes use of the performance tools in LTT to help identify the performance bottleneck.

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=lpg50167&locale=en_US

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=lpg50460&locale=en_US

Post your findings here if you need further help.

Cheers,

Dave Dewar
Asim_5
Frequent Advisor

Re: Poor performance on DLT Drive !


Hi

DAT drive is TLZ-10
DLT drive is 40/80 GB Tape Drive

Rest of the system activities are fine but DLT performance is very poor.

Asim
Dave Dewar
Trusted Contributor

Re: Poor performance on DLT Drive !

Hi,


Ok, your drive specs are as follows:

DAT drive is TLZ-10
1.2 MB/sec or 4.2GB/hr (native); up to 2.4 MB/sec or 8.4GB/hr with 2:1 compression.
12GB native, 24GB with 2:1 compression.

DLT drive is 40/80 GB Tape Drive
6 MB/s or 21GB/hr (native), up to 12 MB/s or 42GB/hr with 2:1 compression
40-GB native capacity, 80 GB with 2:1 compression

Since the DAT drive finishes in 3 hours and your backup size is 24GB and you are only using one tape, your data must be compressing at least 2:1

Its possible that your system performance, disk access to tape is not fast enough to keep the DLT streaming, please use the tools and trouble shooting guides I posted to help check out your system performance. If your system checks out ok then it could be an issue with the DLT drive.

Cheers,

Dave Dewar
Nagarajan Balakrishnan_1
Frequent Advisor

Re: Poor performance on DLT Drive !

Asim,

There is a high possibility that your backup script could be the problem maker. If you are using native tools to backup like "cpio, tar, etc.) you used sufficient buffers to have the streaming happening faster. Send the backup script especially these commands and the arguments. May be you can tweak them to improve the backup performance.

Cheers
Baalki
Asim_5
Frequent Advisor

Re: Poor performance on DLT Drive !


Hi

Following are the commands using for backup. Operating System is VMS 7.3-1

$ show time

$ write sys$output "Initializing Tape"

$ init/media=compact XYZ$MKB500: ABC

$ mount/for/media=compact XYZ$MKB500: ABC

$!

$ write sys$output "Backup co Started"

$ backup/lo/media=compact/ignore=interlock $1$dga16:[KLM]co.bck;* XYZ$MKB500:[000000]co.bck/save/label=ABC


Regards

Asim
Nagarajan Balakrishnan_1
Frequent Advisor

Re: Poor performance on DLT Drive !

Sorry to disappoint you Asim. I dont know about the VMS operating system.

Please refer this to any VMS expert who can comment on the buffers used for backup and suggest ways to increase it.

Cheers
Baalki
Tom O'Toole
Respected Contributor
Solution

Re: Poor performance on DLT Drive !

Try adding /blocksize=64512 (or similar blocksize). BACKUP's default blocksize for tape
is 8192 bytes, very small for today's faster gear. Let us know if this helps.
Can you imagine if we used PCs to manage our enterprise systems? ... oops.
Asim_5
Frequent Advisor

Re: Poor performance on DLT Drive !

hi

will someone tell me how to change the block size. the default buffer size is 512.

regards

Asim
Dave Dewar
Trusted Contributor

Re: Poor performance on DLT Drive !

Hi,

Afraid I am not a VMS expert either, however a block size of 512 is far too low for streaming operation on the DLT drive and is also limiting the DDS drive somewhat as well.

From the first link I posted here is the entry regarding block size:

All DLT products are optimized for use with large block sizes. Block size specifies the size of the chunks of data written onto tape.
ISSUE: Block sizes of less than 64 KB for DLT1/DLT VS80 and 32 KB for all other DAT and DLT drives can drastically increase the backup/restore time and severely affect the performance of the drive.

The link then goes on to describe how to alter block size in the popular ISV apps, unfortunately VMS is not covered.

Cheers,

Dave Dewar
Uwe Zessin
Honored Contributor

Re: Poor performance on DLT Drive !

Just ignore the 'default buffer size is 512'.

Tom already gave an example how to ammend the BACKUP command with /BLOCK_SIZE.

I would, however, use 32256 as a block size, because you then have the ability to transfer the saveset to disk, which is not possible with any higher size.

You should also check your account's process quotas. There are instructions in the OpenVMS documentation on how to properly 'tune' for efficient backups.
.
Tom O'Toole
Respected Contributor

Re: Poor performance on DLT Drive !

Amin,

I probably wasn't clear enough before, you
just add the /block_size qualifier to your backup command:

$ backup/lo/media=compact/ignore=interlock $1$dga16:[KLM]co.bck;* XYZ$MKB500:[000000]co.bck/save/label=ABC/block_size=64512


Uwe is right about 32256 being the largest saveset blocksize which will allow you to transfer savesets to disk. For example, to copy all tape savesets to your default disk
directory, you would do:

$ mount/over=id/block=32256 xyz$mkd500:
$ copy xyz$mkd500:*.* *

However, you should check the relative performance of the smaller blocksize, and weigh the tradeoff of performance .vs. having the ability to copy savesets to disk before you decide to use the smaller.


I also noticed you are copying the files co.bck;* to a tape saveset also called co.bck. This will give a backup saveset container file called co.bck, containing all versions of [klm]co.bck. Are you sure this is what you want to do?
Can you imagine if we used PCs to manage our enterprise systems? ... oops.
Asim_5
Frequent Advisor

Re: Poor performance on DLT Drive !

HI TOM

OK i will take the backup by increasing the block size and will let you know. we already take the backup on disk on we are saving this saveset on DLT.

Regards

Asim
Asim_5
Frequent Advisor

Re: Poor performance on DLT Drive !

Hi everyone

Thanks for all of your support. The issue has been resolved by changing the block_size to 64512.

Thanks and warmest regards

Asim