Less space on LTO5 tape. Tape worn out? Dirty heads?

[Krishius]

Hi everyone!

I just had a situation where I cannot get even the guaranteed amount of uncompressed data (1434 GB) to LTO5 tape using LTFS v2.1.1 on CentOS.

I tried two different tapes - both were rather new (6-7 full rewrite passes) and result is the same.

In the beginning I was able to fill them with 1556 GB of data (which compresses a bit) with around 10 GB of free space left on the tape. Now, I'm trying to get the same data with slight modifications in naming only (no changes in file sizes) to the same tape and writing session ends with error message that says there is no more free space on the tape. Usually, when there is not enough free space, CentOS does not allow me even to start copying data to tape, so therefore first I copy the guaranteed amount (less than 1434 GB), and after that I see how much LTO has compressed the data/how much free space I have left on the tape, and copy the rest to get the tape full.

However, now I start copying less than guaranteed amount of data to tape (a portion of 1210 GB) and close to the end of copying I get error message that there is not enough space on the tape. What is also strange, after that, when I open the properties for this tape, space remaining is shown as "unknown". So, I am not able to copy even the "uncopressed" amount to the tape. What can be reason for this? Bad tape? Dirty heads?

The tape drive is external HP Ultrium 3000 SAS, and tape is HP LTO5 RW. Is the drive supposed to warn me if the heads has to be cleaned? There are "Clean", "Tape", "Drive" lights on the panel but I have never seen them on during operation (except for startup of drive, when they all are on for a while).

Thank you!

K

[Krishius]

Update:

Just performed cleaning with HP cleaning tape (even though the drive did not requested any need for head cleaning) and after that tried to write the same data (1.3 TB) to two tapes - result was 37 GB (140 vs 177 GB) difference of space remaining between those two copies. Both tapes were brand new, also the cleaning cartridge was brand new.

The drive itself is not heavily used. See the attachment picture which shows LTO device diagnostics (screenshot was taken before I performed head cleaning).

Before this problem started, I sometimes noticed some few hundred MB difference in remaining space, which did not seem a problem, but certainly not so many GB.

Still no clues, where might the problem hide?

[Kirill Bogdanov]

Did you try to write incompressible data on the tape, such as photographs? Suggesting because your compression is 8.2 to 1 according to your screenshot which suggests that the drive compresses data so much as to stop and having to repostition (which is extra wear and may cost you GB). You can check the number of repositions in the LTT output.

[Krishius]

Thanks for reply!

I tried to write two tapes full of nearly incompressible MPEG-2 video files (of the Sony XDCAM EX video camera), and the problem still persists.

As I mentioned in my first post, I had already once written the same files on two tapes (two identical copies) few months earlier, therefore I know that each tape can handle certain (identical, at that time) amount of such data.  Now I just changed the naming of the same files, and tried to write them to the same tapes again, and they didn't fit onto tape anymore, and what is even more strange - each of two tapes had noticeably different capacities. Tried brand new tapes - the same. And those were all MPEG-2 video files, so the drive compression ratio should be very low.

Thanks,

Kriss

[Kirill Bogdanov]

It seems we have a similar problem. I'm getting 2-5% capacity loss on new tapes using LTO4 (according to LTT).

Prior to getting LTO4 I've been using LTO2 for a while and occasionally one of the wraps would record not so well; re-writing such a tape would help. It is hence possible that the loss you are experiencing would change every time you rewrite the same tape but I do not know what you can do to recover the lost capacity.

In my case, I'm thinking of either inspecting the drive for dust or failing that trying a new head. The head option is rather expensive hence it would be the last resort.

[Krishius]

So you would suggest me to carry the tape drive to service? It still has valid warranty.

[Kirill Bogdanov]

Call HP and ask them why the capacity was lost, they will ask you questions and should be able to suggest something definite. I think their service should be free of charge since the drive is under warranty. They can even replace it next business day if needed.

Edit: If they offer to replace, there is always something to think about since a replacement is likely to be a refurbished unit and would have likely been used rather more than yours.

I cannot do the same since the warranty on my LTO4 expired.

[Krishius]

Contacted HP support and got my whole tape archival system (Proliant server + HP LTO-5 drive) tested. Looks like the tape drive and tapes are fine. The SAS cable is suspected to be faulty, so I will get it replaced and see if it works.