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DLT Advice Needed

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Doug_3
Frequent Advisor

DLT Advice Needed

Hi, we have 2 rp7400 and 7410 servers (n9000/800 towers). They currently have DLT 7000 drives. Is there an DLT upgrade available that offers faster throughput?

I noted there is an DLT80 drive but I did not find any specs to suggest greater performance.

Thanks in advance.
Doug
4 REPLIES
A. Clay Stephenson
Acclaimed Contributor
Solution

Re: DLT Advice Needed

Not really. You can do things like ensure that each DLT7000 uses a dedicated SCSI bus but if you are really crunched for performance then its time to consider faster technology (e.g. LTO/Ultrium). DLT technology is quite dated now although it still offers good performance.

Your drives themselves may actually be fast enough but your problem is that they are not being fed data fast enough to keep them streaming. If that is the case, DLT's suffer a 10X-100X performance it. Conventional backup tools like tar and cpio simply can't feed data fast enough; fbackup will do a much better job as will Data Protector.

Newer technologies like LTO adjust the speed to match the data so that the data feed rate does not have a drastic performance impact.


My own experience has been that no matter how fast your backups are, it's not fast enough so you need to rethink your entire backup strategy. For example, you might shutdown an application, create a vxfs snapshot for each related filesystem, restart the application, and then backup the snapshots. Because the application is up and running in at most a few minutes, the actual speed of the backup is unimportant.
If it ain't broke, I can fix that.
Steve Lewis
Honored Contributor

Re: DLT Advice Needed

Yes, the DLT80, DLT8000, or DLT8 faster than a DLT7000 (6Mb/sec native uncompressed raw data) and holds up to 40Gb raw/80Gb compressed.

However, DLT is obsolete technology. My advice it to keep your current 7000 so that you can restore from old tapes and instead plumb for a new LTO 2/3 drive. MUCH FASTER and holds a lot more data.

The downside to LTOs is: the tapes are more expensive, they aren't compatible with DLTs, the LTO1/2s need fast storage, they also need fast CPUs to stream the data quickly enough.

We replaced an old DLT8000 with an LTO1 / model 2x0, which is slightly cut-down and slightly slower, but still quicker than a DLT8. The backups started going a lot quicker and we haven't had any problems in 2 years with it. Super. We also have bigger LTOs which do a sterling job.


Pete Randall
Outstanding Contributor

Re: DLT Advice Needed

Doug,

Above your DLT7000 (35GB compressed @ 5MB/s) would be the DLT8000 (40GB compressed @ 6MB/s). The DLTvs80 only had a capacity of 20GB @ 3MB/s. If you really want to upgrade, consider the super DLT or SDLT. There is a SDLT320 that holds up to 320GB compressed and a SDLT600 that holds up to 600GB compressed:

http://h18006.www1.hp.com/storage/tapestorage/dltsdltdrives.html


Pete

Pete
Bill Hassell
Honored Contributor

Re: DLT Advice Needed

Tape drive performance is summarized here:

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&objectID=c00028345

NOTE: DLT 70 is 5 Mb/sec (18 Gb/hr) but a DLT 80 only runs at 6 Mb/sec (21 Gb/hr). So there is no point in replacing the DLT 70 with a DLT 80 since you get maybe 20% better performance.

DLT is like DDS technology -- end of product life. The new technologies are the Ultrium family where the Ultrium 460 can run at 30 Mb/sec (108 Gb/hr) or the Ultrium 960 which runs at 80 Mb/sec (280 Gb/hr). Note that these are uncompressed rates. *IF* and only if your data happens to be compressible, you might see higher throughput.

Now these drives are so fast that many systems cannot possibly keep up with the tape drive. It will be impossible to keep the 960 streaming (running full speed) with an archaic single threaded tool like tar or cpio. fbackup can be configured to maximize throughput (as Data Protector will do too) but this still depends on how fast the data can be pulled from the disks. Since it is so common for systems to be too slow to keep the Ultrium drives streaming, Ultrium drives will actually slow down the tape and heads, down to as slow as 20 Mb/sec.

This article will detail just how fast (or slow) these new tape drives are and ways to test them:

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=lpg50460


Bill Hassell, sysadmin