Really bad performance from software RAID 0

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Level 1

99 points

Really bad performance from software RAID 0

Hi everyone.

I have 2x Samsung 750GB drives in the internal trays connected to the MB controller. These drives are in a RAID 0 configuration using Apple's software RAID from disk utility. I'm having really poor performance -- like 0.5MB/s read and 6.5MB/s write reported by Blackmagic Design Disk Speed Test utility. There is only about 330GB on the RAID volume, so ~20% full. My single boot drive (also in an internal drive tray) runs quite a bit better like 35MB/s read and 45.6MB/s write (I don't remember the actual numbers right now.)

I'm stumped. I'm about to delete the RAID, test each disk individually and try again. Anyone have some better thoughts?

Thanks,
Tim

Dual Xeon 2.8GHz, 16GB RAM, 8800GT, Mac OS X (10.5.8)

Posted on Nov 4, 2009 9:27 AM

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Answer 1

The hatter

Level 9

61,031 points

Nov 4, 2009 11:17 AM in response to Tim Damon

Samsung F1 RAID Edition?

I agree with your plan:

Backup and zero both drives. Do a surface scan. If you have Windows or Samsung BootCD (not sure if it is a Linux CD) I'd do an extended test.

Could these be different models? same firmware? how old?

If you need a pair, Samsung's F3 1TB $93 each.

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Answer 2

Tim Damon Author

Level 1

99 points

Nov 4, 2009 12:07 PM in response to The hatter

Thanks for the thoughts -- I hadn't thought of doing the surface scan on Windows. I bought the drives when I bought the Mac in early '08 and don't think I splurged for the RAID edition -- but they are F1. They were purchased from Newegg at the same time, so pretty sure they are from the same lot.

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Answer 3

Tim Damon Author

Level 1

99 points

Nov 5, 2009 5:46 AM in response to Tim Damon

So I tested the speed after deleting the contents of the RAID and got the same results. I deleted the RAID, formatted both drives and tested them individually with good results. Created the RAID again and now get 120MB/s read and 156.5 write. Which is expected based on the results from each drive's results.

So no clue what happened, but rebuilding the RAID corrected the problem.

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Answer 4

The hatter

Level 9

61,031 points

Nov 5, 2009 6:17 AM in response to Tim Damon

Glad it worked. I always go through those steps I mentioned before using a drive. And it does usually make a difference. Especially the using Samsung or WDC's utility (Windows or BootCD).

Could have been a bad sector. If the partition table develops a bad sector those can only be mapped out during creation, and during creation those hidden partition blocks are tested.

Whenever there is a new OS version or there have been changes to the underlying RAID tools, another good time to rebuild volumes.

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