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RAID Array Spanning Two Channels?
I am rebuilding a PowerEdge 2800 with a Perc 4e/Di array and 2x4 backplane. I was really surprised to find that I could create a logical drive with physical drives from both channels. Now this begs the question, is that something I should do?
I have 8 300GB drives and intended to create two RAID 1 arrays on channel 0 and a RAID 5 on channel 1. The two RAID 1 arrays would have pretty light I/O (OS and system software on one, user homes on the other) but the RAID 5 will have heavy file server usage from about 150 users.
Thinking strictly about paths it seems like I would best utilize my two SCSI channels by having all three arrays split between the two channels instead of leaving channel 1 to do all the heavy lifting. What I don’t know is if you take a performance hit by spanning channels like that or if there are any other reasons why that might be an undesirable configuration.
pcmeiners
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Posted October 18th, 2008 12:00
A U320 channel will max out throughput at <5 drives under heavy load due to SCSI bus saturation. Dividing your arrays over two channels will increase your thoughput... no negatives in dividing arrays over two channels, except, even with drive roaming, drives located on one channel can not be moved to the other channel; if you mark your drives as to slot and channel this should not happen. Dividing arrays over multiple channels is the standard, placing them all on one is not.