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Query about DLT performance

by jconner / August 15, 2007 3:15 AM PDT

I've moved this from the LINUX forum to here because 1) no one answered and 2) it may well be a PC hardware issue.

The PC is a Dell Optiplex 745 running SUSE 10.1 LINUX with a DELL 120T DLT7000 autoloader connected via an Adaptec AHA2944UW SCSII PCI card (supports up to 40MB/second). Its a stock DELL except for the 2944 card and installing SUSE over XP.

The DLT drive is rated to 35GB uncompressed.

I normally backup around 13 - 15 GB per tape and never in compressed mode. The tar backup takes about 1 1/2 hours to complete. The verify read (directory file list only) take between 3 and 4 times as long to complete.

I am using new Fuji DLT Tape IV tapes.

I've tested this on several SUSE machines with similar interfaces and get roughly equivalent results as well as with other DLT 7000 drives.

This seems extremely slow write and read given the stated transfer rate for DLT 7000 series drives of 5MB/second sustained.

Am I missing something on tar -t -v? Or is this a hardware issue? Is this what I should expect in terms of performance?

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by ozos / August 15, 2007 6:46 AM PDT

would give you roughly 18,000MB/hour, so you're getting roughly ideal performance in writing 13-15GB uncompressed in ~90 minutes

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I didn't know people still use tapes...
by ahtoi / August 15, 2007 5:00 PM PDT

Maybe it's about time to upgrade.

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not really
by ozos / August 16, 2007 1:01 AM PDT

A lot of major industries still use tape, its what StorageTek still makes money doing, tape is less expensive per GB on the mass basis (we're talking petabyte range here) which helps with large archives.

Upgrading for the OP would probably require at least 2 or 3 new hard-drives.

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Just sharing.
by R. Proffitt Forum moderator / August 15, 2007 5:03 PM PDT

I've seen that issue as long ago as 20 years ago. It has to do with the tape reading, stopping, backing up, up to speed, etc.

Not broken, just not well tolerated.


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for all
by jconner / August 16, 2007 5:57 AM PDT
In reply to: Just sharing.

We use tape for permanent offsite or project archival that won't fit on optical.

The issue for us seems to be the slowness of a verify (not a restore) vs. a write. 4:1 difference in performance.

We also use Exabyte 8MM and 3590 cartridge and neither seem to exhibit such a differential. The 3590 is only 5GB and the Exabyte is only 2.5GB uncompressed.

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Just sharing.
by R. Proffitt Forum moderator / August 16, 2007 6:32 AM PDT
In reply to: for all

That 4 to 1 speed on directory reads has been with us for decades. Nothing new, nothing broken.


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Just sharing - Thanks Bob and all
by jconner / August 16, 2007 9:44 AM PDT
In reply to: Just sharing.

At least it is a known issue. We're into Terabytes of online storage and soon to be 100% redundant online backup. However still faced with offline and project backups requiring removable media. Does this issue map to newer & higher density DLT's?

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For directory reads? Yes.
by R. Proffitt Forum moderator / August 16, 2007 9:58 AM PDT

At least full restores run at top speed.

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