How many bad tapes are "normal"?

Question

I use Quantum DLT-S4 tapes (800/1600GB) in my library, which has two Quantum tape heads in it. I have had quite a few bad tapes i.e. tapes that come up "CRC error" or "cannot read tape" etc and the backup software marks them as bad. I've sent back around 20 to Quantum out of 100 for a refund. The library is only 18 months old, and one of the drives has already been replaced a while back. Still get bad tapes. How many bad tapes do you guys get?

score 6 · Accepted Answer · answered May 25 '09 at 04:57

About a year ago I switched the system at my office to a rotating pool of about 80 LTO4 tapes and have only had one tape fail - it was physically dropped though. The rest of the tapes go through backup/restore/verify cycles and have never had an error.

Prior to that we used over 200 LTO2 tapes and had only a single error in the two years I was with the company (the tape errored out while writing to it). For what it's worth both the LTO2 and LTO4 drives are Sun-branded HP Ultriums inside a Storedge L8 and an SL24.

So I'd say 20 out of 100 in my experience at least is ridiculously high, so much that I would be extremely wary of trusting that system to handle a company's backups.

I would suspect that DLT tapes are less reliable than LTO. I've had the same experience of tape failure rates -> DLT ones have started going bad a lot more often than LTOs for us. Perhaps they are more delicate internally? — David Gardner, Apr 26 '10 at 17:29

score 1 · Answer 2 · answered May 25 '09 at 07:01

1

I would expect that answer to be 0, assuming that the tape was used within the limits of rewrites, temperature, storage, etc.

I would start looking at the environment that the drive operates in, or the tapes are stored in.

answered May 25 '09 at 07:01

Dave Cheney

18,567
8
49
56

score 0 · Answer 3 · answered May 25 '09 at 14:04

First, ensure the drive has been cleaned with a fresh cleaning tape.

Second, check for any signs of physical damage on the tapes, some drives and loaders react very badly to even the slightest damage.

Third, at 10% failure from a batch I'd be threatening them with the whole batch back, I'd expect 2-3% at worst.

This does assume that the tapes are at least as new as the library. Even in heavy use tapes should easily last two years.

score 0 · Answer 4 · answered Jun 08 '09 at 20:58

With LTO1, LTO2 and LTO3 I have stack from the last 7 years on my desk and it's only 7 tapes high. That's from a pool of say 800 tapes over the past 7 years. So something right about 1%. Not including one bad batch we got right before I was hired where we sent them all back and swore off that tape manufacturer ever again.

I agree with the drive issue comments though. If your drive is out of alignment or dirty it could surely cause a ton of issues. I'd get a new batch of tapes, see if the problems persist and if they do then call the drive/library vendor and get that squared away.

How many bad tapes are "normal"?

4 Answers4