On Mon, Jun 30, 2008 at 10:17 AM, Christiaan Willemsen < [EMAIL PROTECTED]> wrote:
> The question is: how can we maximize IO by using the best possible > combination of hardware and ZFS RAID? > > Here are some generic concepts that still hold true: More disks can handle more IOs. Larger disks can put more data on the outer edge, where performance is better. If you use disks much larger than your required data set, then the head seek movement will also be minimized (You can limit the seek more by forcing the file system to live in a small slice on the disk, the placement on the disk which you can control.) Don't put all your disks on a single controller. Just as more disks can handle more IOs at a time, so can more controllers issue more instructions at once. On the other hand giving each disk a dedicated controller is a waste because the controller will then be idle most of the time, waiting for the disk to return results. RAM, as mentioned before, is your friend. ZFS will use it liberally. You mentioned a 70 GB database, so: If you take say 10 x 146GB 15Krpm SAS disks, set those up in a 4-disk stripe and add a mirror to each disk, you'll get pretty decent performance. I read somewhere that ZFS automatically gives preferences to the outer cylinders of a disk when selecting free blocks, but you could also restrict the ZFS pool to using only the outer say 20 GB of each disk by creating slices and adding those to the pool. Note if you do use slices in stead of whole disks, you need to manually turn on disk write caching (format -e -> SCSI cache options) If you don't care about tracking file access times, turn it off. (zfs set atime=off datapool) Have you decided on a server model yet? Storage subsystems? HBAs? The specifics in your configuration will undoubtedly get lots of responses from this list about how to tune each component! Everything from memory interleaving to spreading your HBAs across schizo chips. However much more important in your actual end result is your application and DB setup, config, and how it is developed. If the application developers or the DBAs get it wrong, the system will always be a dog.
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