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I have a simple RAID at home with 2 mirrored drives and for some reason I cannot get any sort of performance out of them... Running hdparm -t I consistently score about 100MB/s, but I get 250 to 300 from my laptop! What am I doing wrong?

Setup:

  • Dell 2850 2U
  • Intel srcs28x SATA hardware raid
  • 2 2TB SATA II or III drives
  • Running one logical mirrored drive:
  • adaptive read ahead
  • write-back
  • direct i/o
  • drive caching enabled on both
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migrated from serverfault.com Nov 4 '11 at 5:03

This question came from our site for professional system and network administrators.

2 Answers

Write speeds like that on your laptop are either because you have an SSD or caching is playing a part. A single good quality SSD will outperform a SATA disk by a substantial margin.

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well these numbers are garbage. Is there no way to improve them? I could have sworn they were higher... –  Eric Fossum Nov 4 '11 at 2:23
    
100MB/s is garbage? Have you looked at benchmarks for those drives to know what to expect? –  MDMarra Nov 4 '11 at 7:24
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You're running the wrong raid type (RAID1) if you're looking for performance. Read performance on RAID1 can be faster than a single drive as data is copied in more than one place and therefore two simultaneous reads can occur, however write performance on RAID1 is still realistically no faster than a single drive.

RAID0 offers the best performance for your $ but a failure of a single drive means catastrophic data loss. For the best balance of speed+fault tolerance, consider RAID10, which has a minimum requirement of 4 drives.

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before I migrated to RAID 1 with two drives the single drive would write/read at around 20-40MB/s over the network, now I get 3-4MB/s. There has to be something wrong, I think I'll send Intel a service request because this is nearly unusable. –  Eric Fossum Nov 4 '11 at 15:50
    
Well now you're talking about a whole different animal with network transfer speeds. A bunch of factors can affect that. Buffered disk reads of 100MB/s is what I would expect from a RAID1 array of standard SATA II drives. –  Garrett Nov 4 '11 at 16:24
    
Well I'm 90% sure it's a raid issue because of lags seen on the system and how disk intensive activities seem to take much more CPU than they should. –  Eric Fossum Nov 5 '11 at 22:30
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