Thanks Constantin, that was just the information I needed!
Trev Constantin Gonzalez wrote:
Hi,I have a shiny new Ultra 40 running S10U3 with 2 x 250Gb disks.congratulations, this is a great machine!I want to make best use of the available disk space and have some level of redundancy without impacting performance too much. What I am trying to figure out is: would it be better to have a simple mirror of an identical 200Gb slice from each disk or split each disk into 2 x 80Gb slices plus one extra 80Gb slice on one of the disks to make a 4 + 1 RAIDZ configuration?you probably want to mirror the OS slice of the disk to protect your OS and its configuration from the loss of a whole disk. Do it with SVM today and upgrade to a bootable ZFS mirror in the future. The OS slice needs only to be 5GB in size if you follow the standard recommendation, but 10 GB is probably a safe and easy to remember bet, leaving you some extra space for apps etc. Plan to be able to live upgrade into new OS versions. You may break up the mirror to do so, but this is kinda complicated and error-prone. Disk space is cheap, so I'd rather recommend you safe two slices per disk for creating 2 mirrored boot environments where you can LU back and forth. For swap, allocate an extra slice per disk and of course mirror swap too. 1GB swap should be sufficient. Now, you can use the rest for ZFS. Having only two physical disks, there is no good reason to do something other than mirroring. If you created 4+1 slices for RAID-Z, you would always lose the whole pool if one disk broke. Not good. You could play russian roulette by having 2+3 slices and RAID-Z2 and hoping that the right disk fails, but that isn't s good practice either and it wouldn't buy you any redundant space either, just leave an extra unprotected scratch slice. So, go for the mirror, it gives you good performance and less headaches. If you can spare the money, try increasing the number of disks. You'd still need to mirror boot and swap slices, but then you would be able to use a real RAID-Z config for the rest, enabling to leverage more disk capacity at a good redundancy/performance compromise. Hope this helps, Constantin
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