08-09-2011 07:57 AM
I have a few LTO 4 drives. I noticed that apart form some software errors on some media many tapes have utitlization below 800 GB ( like 500, 600 ). This happens even on new tapes. I made soem Write-Read tests in LTT. Example of log :
_ Writing data (3.8 GB/ 4 GB)
| |__ Writing data (4.0 GB/ 4 GB)
| |__ Total amount of data written : 4 GB
| |__ Rewinding
| |__ Checked CCQ write and re-write values (Written: 0x30177, ReWritten: 0x64A0)
| |__ Capacity Loss is 13
| |__ Performing 1st read phase of read/write test
| |__ Reading data (0.0 MB/ 4 GB)
| |__ Reading data (256 MB/ 4 GB)
| |__ Reading data (512 MB/ 4 GB)
| |__ Reading data (768 MB/ 4 GB)
Can someone explain why capacity loss is greater than 0 ? Is it normla and can be a cause of not fully allocated tapes. On another drives I have always 0 on this test - using the same tape .
08-10-2011 12:09 AM
Whenever the tapedrive encounters a problem writing a data block to tape, it will rewrite that block again. This is how the LTO technology is designed. Consequently, if a drive encounters a lot of these 'rewrites', extra space on tape is consumed which can lead to loss of capacity on tape. Makes sense ?
in your test case:
Written: 0x30177, ReWritten: 0x64A0
the drive had to rewrite 25760 blocks out of the ~200000 blocks it wrote to tape which equates to 13%
The question now becomes, is this a tape problem or a drive problem ?
Best step is to rerun the test with a new(!) tape and examine the results. If the number of rewrites still is high, contact HP support and suppy them with a support ticket created Library and Tape Tools. If the number of rewrites is low with a new tape then you best discard the tapes producing these rewrite rates. After all, tapes wear down faster than drives.
good luck and take care,
08-10-2011 01:23 AM
Thanks for explanation.
As you suggest my main question is : tape or drive problem.
This test was done with brand new tape. I just wonder if this rate is acceptable - do you consider it high ?. WIth some older tapes I get even 20 - 30 % capacity loss on those suspected drives.
On another healthy drive tests with the same new tape and older tapes always show 0 %.
Supporting is saying that there is no hardware errors on suspected drives and they suggest that problem is with tapes. So I am stuck at the moment - but this is not accpetable for me to have such a loss of capacity on many tapes.
08-10-2011 03:54 AM
Well, you paid to have 800GB per cartridge natively. While I understand that some capacity loss may happen over time as the drive ages, personally I think anything over 10% is an issue as we lost 80GB of tape capacity in this case. (if you have 100 tapes in the library that equates to 8000GB ~ almost 8TB !)
Note: the drive is doing well considering that it is still storing your data on tape without complaining (..right ?..) but obviously there is an issue with the drive based on your description.
I think your next step should be to tell your HP Support engineer what we discussed here.