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kashani wrote: |
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> Sean Cook wrote: |
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> |
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>> This is not necessarily the case, typically if you are CPU bound then |
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>> the above statement is true. If you are IO bound, then software raid |
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>> offers, overall, better throughput to the disk and allows for more |
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>> flexibility. |
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>> |
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>> Back in the day... we were running the LSI MegaRAID controllers with |
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>> RAID 1 on 9gig SCSI disks, we were choking our application |
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>> (mysql/mod_perl) we took the MegaRAID controller out and performance |
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>> increased by about 25%. (note: this is a real world situation) |
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>> |
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> |
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> Then you my friend had some seriously broken hardware. I've never seen |
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> anything get slower by moving to dedicated RAID card and usually it got |
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> 2-3x faster due to having a dedicated local cache on the card. |
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No... there are plenty of people who have experienced the same thing... |
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infact, http://linas.org/linux/raid-reviews.html |
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shows that the through put is more that 5x's the speed of the hardware |
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raid. |
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|
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Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU |
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K/sec %CPU |
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(DPT hardware RAID5, 3 disks) |
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DPT3x4G 1000 1914 20.0 1985 2.8 1704 6.5 5559 86.7 12857 15.6 |
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97.1 1.8 |
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(Linux soft RAID5, 3 disks) |
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SOF3x4G 1000 7312 76.2 10908 15.5 5757 20.2 5434 86.4 14728 19.9 |
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69.3 1.5 |
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Redhat In their manual: |
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"With today's fast CPUs, Software RAID performance can excel against |
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Hardware RAID." |
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As I stated before, it depends on where your bottleneck is... if you are |
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not cpu bound, software raid is great! and will boost IO through put on |
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comparable hardware. If you are already CPU bound, forget software |
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raid, it will degrade your system to a crawl... |
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|
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Sean |
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=RtK2 |
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