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Optimal Raid Setting For Small Transfer/queue

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The server is an IBM x235 with 6 disks, some 10k RPM IBM (Ultra320). Currently I have two RAID sets, one RAID 10, and a RAID 50E. All six disks are on the same channel.

First of all, what 'effect' does it have, having all six disk on one channel? Using the configuration tool, it seems that there are two channels in total on the RAID adapter.

Secondly, what does it mean that the logical drives are in 'Write Back' mode, while the actual hard drives are in 'write through' mode?

Thirdly, what does it mean that ServeRaid reports 4 'physical slots' what is that compared to say channels?

I've tried to measure the performance using IOMeter, which does show 'superior' performance of the RAID 50E compared to the RAID 10 setup, but the problem is that it only surpasses the RAID 10 when the queue length increases above 2 or 3. Using perfdisk, the average queue lenght is around 1, so it seems that it does not really matter what RAID setup I choose to use. Is there a way to optimize the RAID 50E to perform better with small queue lengths?

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