SDLT reliability

[Kari Uusimäki]

Hello All,

There are a few things to remember when dealing with tape drives and keeping up the reliability of backups and restores.

Do use cleaning tapes every time the drive asks for it. The more you use new tapes, the more residue will be emitted from them on the read/write head. More used tapes emit less residue. You can run a cleaning several times consecutively if needed. Do _never ever_ overuse the cleaning cartridges!

Handle tapes as specified (=carefully). Don't forget to do "retensioning" regularly.

Update drive (and library) firmware when new versions become available. Firmware updates do correct problems and makes drives more reliable. They are not made just for fun. One tool you can use yourself for firmware updates is HP LTT. If unsure, do call HP support for assistance.

Some DLT or SDLT tapes might have quality problems. I've seen that also.

When keeping drives in good shape, there won't be much problems and tapes last longer, too. I don't mean that somebody neglects necessary servicing of his drives, but what I want to point out is, that servicing them is very important, because newer drives have very tight tolerances and a lot smaller deviations can cause problems where they weren't seen before with earlier drives. The data density on the tape has grown enormously since when DLT technique was introduced back in '85. At that time you could write 95MB of data on a tape. The newest SDLT tape will hold 600GB of data (over 6000 times more) and the tape is roughly the same. No wonder it is important to care for the drives so they can accomplish their task.

The same discussion goes for LTO drives and tapes. They are similar to DLT and SDLT drives in many ways, even though LTO technique is only a few years old.

With over 15 years of experience with tape drives, I would say that DLT, SDLT and LTO drives are quite reliable.

Good luck with your backups and even more with the inevitable restores!

Kari

[Dan Rolsma]

YES! SDLT has been horrible. SDLT220 was worse than SDLT320. I bought an MSL5026SL, which was replaced once, and then again with a MSL5026S2 all under warranty. Once the budget allowed, WE THREW IT AWAY (went to auction actually)! Tape drives, I forget how many we went through, 8, a dozen. I lost count. At one point HP hardware support told us a 20% tape failure rate is normal (!). I didn't accept that. That is our backup system! Good thing our servers were more reliable. Not a comfortable position to be in. Out of 2500 DLT tapes, we had 2 failures.

We replaced the HP (Overland Data was printed inside on all the circuit boards) with a StorageTek L80, which is 80 percent better. We still go through tape heads, but the library itself is more reliable. The tape heads also work, or they don't, which was a refreshing change. Under HP, sometimes yes, sometimes no. Wait a day and see. Was it the tape? The drive? The SCSI card? Oh, another firmware update, I see. We were always chasing our tails with intermittent problems.

We recently discovered how to put the leader back into the sdlt drives so we don't need to wait for an overnight replacement. We put the leader back in in 10 minutes, once or twice a month. We got a bad batch of tapes not packaged properly and were damaged in shipment, internal damage so I can't tell until the tape causes the tape drive leader to pull out. I tried to work with the vendor to get the tapes packaged properly but had to change vendors.

I just ordered an L80 with HP LTO-3 drives. If they work out, no more sdlt. We could replace all the sdlt drives with LTO drives - because we bought the L80 which is upgradeable. It can even run sdlt and lto at the same time in the same library. Not so with an HP library. Having each available is great for transferring what can be read from the sdlt onto LTO - without buying an entirely new library.

Dan.

[Dan Rolsma]

Steve,

To add to my last post, I verify our tape backups - which causes twice the wear of course, but that is when I've found many problems. I presume that most sites, which do not recheck tapes periodically, or don't notice a tape only filled up part way, may think there is no problem. They just rely on the backup software to signal a problem - and some day they may have a rude awakening when they try to restore an entire system from a particular date.

Dan.