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fleecy

Normal SAS Speed is?

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I installed my first SAS-based backup system yesterday.

 

Power Mac G5 Quad Processor, Leopard 10.5.6, 4.5 GB RAM

ATTO ExpressSAS H380 (purchased after getting a recommendation from EMC tech support, since no SAS adapters are listed in their database)

HP Ultrium LTO-4 1760 SAS external drive

 

Latest Retrospect 6 version, latest driver update was applied too (necessary to get SAS support)

 

Backups seem to work reliably so far, but I only see copy speeds of about 500-600 MB/min from Retrospect.

 

This is much, much slower than the 1800 MB/min speeds I can see with a nearly identical Ultrium 1760 drive, this time with a SCSI port and hooked up to a Dual 2.3 GHz G5, 2.5 GB RAM, OS X 10.4.11 through an ATTO UL4S.

 

Is this a SAS limitation? Isn't SAS very similar to SCSI?

Edited by Guest

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You don't provide any information regarding the H380 firmware and driver numbers; there was an ATTO firmware update and driver update for the H380 less than two weeks ago (H380 driver 1.14, H380 firmware 2009_01_26). Have you tried that update?

 

You might want to call ATTO tech support, perhaps they can help you tweak the settings.

 

You might also want to see if HP has a diagnostic tool that will let you write big blocks to the drive so that you can see an upper bound for the transfer rate.

 

You don't say the speed of the G5 Quad, and you don't say whether the source is the same in both tests.

 

You also don't say anything about the H380 firmware version. Has that been updated?

 

It would also be helpful for posterity to provide the Retrospect version and Retrospect RDU version you have. "latest" isn't helpful because these posts persist for years, and someone else, researching a similar issue, wouldn't have a clue what versions you have tried.

 

Russ

Edited by Guest

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Retrospect 6.1.230 is installed in both cases, along with Driver Update 6.1.15.101.

 

The G5 processor speed is 2.5 GHz.

 

Source for backups : in both cases, they are communicating with Retrospect Client for Mac 6.2.234 on Intel Macs running Leopard 10.5.6. Local backups (backing up the server's boot drive, for example) results in the same speed difference, so I assume that network issues are not in play here.

 

I applied the latest firmware (January 26 2009) from ATTO to the SAS card right after installing it in the G5. The OS X driver for the ATTO card is the one you mention, too.

 

I'll give the ATTO tech support line a call, maybe they have ideas. Thanks!

Edited by Guest

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Well, network issues would/could be in play to the Intel Mac clients, but the significant point is that you are seeing the same speed difference for a local backup of the server's boot drive. That's the only meaningful test.

 

Ok, another question. Are the sources similar when backing up the local boot drives?

 

Possible differences:

 

Perhaps the drives on the two G5 processors (dual and quad) are of different speed. Check that.

 

Is the boot drive on the faster (dual) G5 a RAID 0 (boy, that would scare me) or a RAID 5? That would give it faster speed than an unraided boot drive.

 

Try doing a timed dd to /dev/null on the respective sources to see if there are significant differences:

time dd if=diskname of=/dev/null bs=1m count=10g

 

You will need to do the test on a volume that is not in use, such as an unmounted partition.

 

Russ

 

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