drescherjm

Poor software raid5 performance in XP

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I have used linux software raid5 and raid6 for years and the performance for me is quite acceptable. I have 15TB of linux software raid currently at work using > 50 SATA drives... With linux software raid I expect sequential writes to be at minimum faster than the speed of 1 hard drive. Since the price of drives has gone down to less than $100 for 500GB and most motherboards have fakeraid5 I decided to try this with new computer builds. After playing around with this for a few days I am horribly disappointed with the write performance. One example of this is when transferring a 10GB file over a gigabit network. With a single drive the transfer is less than 5 minutes. With a 3 or 4 drive software or fake raid5 it will take > 25 minutes. From my linux experience the problem appears to be that the cache manager is forcing writes too frequently and the raid subsystem is not caching stripes so that every stripe is being read before it is written back. With linux you can lessen the impact of this by increasing the size of the stripe cache. However under XP I see no way to do that. I did enable LargeSystemCache but that appears to only help for the first few seconds where the gbit bandwidth holds steady at >50% for a few seconds then settles down on 3 to 8%. During all of these tests the cpu usage on the dual core machine with 4GB of memory is less than 10%.

Edited by drescherjm

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Some more testing... nvraid RAID10 is not faster than a single drive at writes in this 10GB test. It is also not faster at reads according to hdtach. It looks like I am going to give up at this and use 750GB Segate 7200.11 drives (in a single drive configuration) I bought for a linux sever in the 4 desktops and 12 x 500 GB drives in the server instead of the 8 750s I was planning...

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