[sclug] Better than RAID?

[Alex Butcher]

On Sat, 1 Oct 2005, Alan Pearson wrote:

> Don't know why you want EVMS for a normal system when LVM2 (part of Suse) 
> would be suffice.

Also, IIRC, EVMS has been deprecated in favour of its unique functionality
being ported to LVM2.

I've been using LVM and LVM2 for about three years now with no significant
problems. The only caution I would raise is that I encountered some
difficulties burning CDs on-the-fly (i.e. 'mkisofs ... | cdrecord ... ')
from post-creation extended filesystems on LVM on Linux software RAID. This
was a while ago, though, so it may have been a bug that has been long fixed.

Regardless, I now burn CDs and DVDs from a plain ext2 filesystem set aside
for this purpose, and I don't create DVDs on-the-fly.

Re. Linux software RAID, I'm turning against it, due to its practice of
removing a device from a RAID set upon encountering a single read error. The
device then needs to be re-added and re-mirrored from the remaining devices
in the RAID set. If one of *these* encounters a read error during the
re-mirroring, well, you're stuffed. :-/

By contrast, when BSD's software RAID encounters a read error, it will
immediately try to re-write the block from the other volumes in the set.
This will probably fix it, but only if it doesn't will the device hosting
the failed block be removed from the set. This strikes me as much safer. BSD
also makes use of extended SCSI return codes to determine when a device
encountered recoverable problems reading a block and will then pre-emptively
re-write that block in an attempt to prevent later problems.

> AlanP

Best Regards,
Alex.
-- 
Alex Butcher      Brainbench MVP for Internet Security: www.brainbench.com
Bristol, UK                      Need reliable and secure network systems?
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