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Re: raidframe performance question

 On 5/13/2011 8:40 AM, Paul Goyette wrote:
Nope. -A simply specifies the alignment of the DOS partitions (and the offset of the first partition). If your drive might have "native" sectors larger than 512 bytes, you need to use this, otherwise all your I/Os will get split across drive-addressable sectors and performance will be very bad (tm) as the drive reads one physical sector, updates and re-writes the latter portion, then reads the next sector and updates the early portion.

Note that most versions of NetBSD's fdisk(8) have a parsing bug, and will not accept "-A 2048" (where the offset is supposed to default to the alignment). Instead you have to specify "-A 2048/2048". I fixed this error as soon as I found it!


I'm trying something a little more advanced and am having some problems.

Instead of trying to do what you did (which does seem to work fine) I'm trying to build a new system on a new RAID-5 array without any "non-RAID" partitions. I'm also doing this from the install CD (and to make it even more challenging, the AMD64 5.1 boot CD).

Before the install, I drop into the shell and do all of the setup for the raid array. I get the array all built and configured, and then drop back into the install program and run through the "normal" steps, but install on the RAID array instead of one of the disks.

Everything works OK until I try to boot. If I set up a small wd0 root partition I can get the boot sectors to boot the RAID-5 array, but if I build the RAID array, use the whole set of disks for the array, and try to boot, I get all sorts of boot problems.

If I set up a minimal install on each of the wd[0-3] drives (since there's no SURE way to predict which drive the BIOS is going to try booting from) and set up the installboot for each, I can get the array to boot with no problems.

Once the array boots up, everything is wonderful, using the 2048 alignment and making sure all of the "logical drives" (raid0a, etc.) aligning on 1M boundaries makes this WICKED fast.

If anyone has any idea how to get the RAID-5 array to boot after the "raidctl -A root" and the appropriate disklabel and installboot directives, I'd love to hear them.


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