Slow restore speed from Ultrium 920 External SAS

[drk14]

Just installed a brand new Ultrium 920 external SAS drive, and running some intitial tests.  During backup of a test directory (using ntbackup on Windows XP Professional SP3), transfer rates were approximately 100 MB/sec, but when restoring a single file from this backup, the transfer rate was only ~10 MB/sec (i.e., ~8 min for a single 5-GB file).  Also, I noticed that during restore, the tape motor would stop and go every second (whereas during backup, the motor speed was approximately constant).

Should I be concerned?  Can the restore speeds be improved?

Thanks

P.S. I would attach trouble ticket file, except I can't get the attachment feature in these forums to work.  What browsers are supported to be able to upload files?

[shivu.h.n]

 Hi Jens K,

Thanks for using HP Forums!

In order to attach a new file in the earlier post,

1) Sign in using your id and password,

1) Click on the Options button located at the right hand side of the post.

2) Select Edit Message options

3) Click on the attachment field provided below the "Post Message" section.

4) Browse and upload your text file.

And if you want to attach in another new post then you can follow the same process by clicking on the Reply button.

Kindly let us know, if you are facing the same problem still!

[drk14]

Shiva,

What I meant was that the process you have described doesn't work for me.  I click "Browse" and select a file (the path to which is then displayed in the Attechments form field); then I click "Post".  This results in the message being posted without any attachment.  I have tried this in IE6 and in FireFox 3.5.

JK

P.S.  Any comments on my original question about the tape drive?

[drk14]

I have done some more testing. 

Using the restore test in L&TT SysPerf (using 2:1 compression), I get:

 18 MB/sec when restoring to the internal D: harddrive;

 30 MB/sec when restoring to an external firewire (FW400) harddrive (!).

During actual restore operations (using ntbackup), I get:

 11 MB/sec when restoring to the internal D: harddrive;

 16 MB/sec when restoring to an external firewire (FW400) harddrive (!).

On a hunch, I backed up a new data set  using the option in ntbackup to disable hardware compression.  When restoring these uncompressed data, I get:

 12 MB/sec when restoring to the internal D: harddrive;

 27 MB/sec when restoring to an external firewire (FW400) harddrive (!).

In all of the non-virtual restore tests, except for the last one listed above, the tape drive was operating in stop-and-go mode ("shoe-shining").  However, when restoring uncompressed data to the external harddrive, the tape drive motor was moving pretty much continuously.  I guess that makes sense, since the minimum transfer rate spec for the Ultrium 920 is 26 MB/sec.

So I am more confident that the poor performance observed is dependent on the computer system as opposed to the tape drive, but the results are still confusing.

- How is my external harddrive getting faster restore speeds than my internal D: harddrive (which is SAS, but on a different HBA than the LTO drive)?  Incidentally, when backing up from harddrive to the Ultrium 920, the internal harddrive gets better performance than the external harddrive (e.g., 52 MB/sec vs. 32 MB/sec for uncompressed data).

- Is it really necessary to disable compression to realize restore speeds greater than 26 MB/sec?  Are there other likely bottlenecks that can be cleared?

Would appreciate any insight available for improving the performance of my system.

Thanks,

drk14