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Re: raidframe performance question

 On 6/15/2011 1:03 PM, David Laight wrote:
On Wed, Jun 15, 2011 at 06:37:58PM +0200, Joerg Sonnenberger wrote:
On Wed, Jun 15, 2011 at 11:23:48AM -0500, Dave Burgess wrote:
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.
The boot loader only supports RAID1 by effectively ignoring it.
Worse than that really!
The code that loads /boot has another look 64 sectors down the disk if
it fails to find it (in the filesystem) at the expected offset
(this skips the RF header).

Booting from RAID-5 would require that the low level boot code understood the
RF parameters. Particularly nasty for raid-5 if one of the disks has died.

Plausibly the code in /boot could understand the RF header - allowing the
kernel (and modules) be read from the raid, but everything earlier
isn't likely to be changed.

Unless, of course, the system bios is able to do it - and the disk number
used requests the raid accesses.

I did once jave a plan to let sysinst install to a raid-1 single disk - to
which a mirrored copy could be later added.
In theory sysinst could install to a real raid-1 without having to rebuild
the raid at all - since the contents of unwritted sectors are 'don't care'.
(OTOH that might be rather connfusing much later on!)


OK - that explains that.

Not to put too much more effort into this, but what would a minimal "boot segment" look like?

I'm sure the /boot loader and the kernel need to be available. What about all of the 'associated' kernel stuff? Would you even need things like "init"? Would the kernel, with kernel modules and RAIDFRAME installed, be enough? I know (from experience - I've built

Also, thanks to the 'automatic RF segment' skipper, there's no reason why you couldn't install NetBSD into a real, no-kidding RAID-1 at boot up - it's simple enough to do and the bootloader works reliably enough for it. I'd support that.

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