Re: Promise or 3Ware? - booting
On Fri, 26 Mar 2004 01:08:50, Alvin Oga wrote:
> On Thu, 25 Mar 2004, Miquel van Smoorenburg wrote:
>
> > The problem with software raid is that if the first (boot) disk
> > goes south, the system won't boot anymore. If you're using RAID1
> > just for data integrity and don't care if you have to open up the
> > machine and replace the disk to get it going again, then that's
> > no problem. If you want to maximize uptime, use hardware RAID1/RAID5.
>
> i've not seen sw raid1 preventing a system boot if either/any disks
> goes down ...
I have.
> - just need to config it correctly .. and test it by pulling
> the ide cable off of the disk under test
That's if the disk is _dead_. What if you have 2 disks in RAID1 mode,
you boot from the first disk, and while the boot sector is OK, the
rest of the disk doesn't respond (bad sectors or whatever). The kernel
won't be started. There, you're dead in the water.
You need to go to the system, and swap the disks physically, before
you can boot again. No data loss, presumably, but downtime.
The only way to fix this is to use either hardware raid, or a form
of software raid supported by the system BIOS. The latter isn't
supported under Linux with 2.6 kernels, so that's not an option.
> - a properly config'd raid setup should still keep working
> even if its in degraded mode
Well even if the first (boot) disk is dead completely, if the BIOS
doesn't support booting from the 2nd disk automatically
(90% of the BIOSes out there don't) you're _still_ dead in the water.
> - raid is NOT a reliable data backup
> raid1 is the worst for data backup..
> ( "rm filename.foo" and its gone from the other disk too
> ( in a matter of seconds
You can't say it's not reliable .. it does _exactly_ what it's
supposed to do. You could use LVM snapshots I guess.
> > I think I should convert our internal dutch documentation to an
> > english MINI-HOWTO one of these days.
>
> whats the url of the dutch version that can be externally accessible ??
It's on an internal webserver that isn't accessible from the outside.
Hang on .. http://www.miquels.cistron.nl/bootable-raid1.html
Mike.
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