July 18, 2006 at 6:22 am
A couple of quick questions... If I am planning an two different RAID's, one RAID1 and one RAID5 and I am concerned about SCSI bus saturation on the RAID5 array, how many channels do I need?
I would think 3+ channels: 1 for RAID1 and 2+ for RAID5 (let's just stick with 2 for this question).
So, do I, in fact, need a SCSI controller with 3 channels? Do I need a special backplane? Can one SCSI controller support two RAID arrays AND split one array over multiple channels?
Thanks. RH
July 18, 2006 at 9:04 am
yes! Well actually it depends upon all sorts of things including internal/external etc. etc.
I'm not sure about using two channels with raid 5, I've done this with raid 10 with external array boxes. However much of this is down to what the array controller(s) will support.
Multiple channels on one card are limited by the bus bandwidth of the server, generally you'd try to use two controller cards in different server buses for maximum throughput. There's also which scssi you're using too.
Check out the Administrators Companion or the performance tuning handbook which explains how to calulate i/o and bandwidth vs numbers of spindles and raid ( may I suggest you forget raid 5 for data < grin > ) especially if you're concerned about performance.
So in short it depends upon what your chosen controller card supports, most support multiple arrays on a channel. Ultimate best practice says set a channel/card per array.
Modern sata stuff does loads of disks per card/port - but I don't have any experience of this.
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