RAID 1 or Hammer
mneumann at ntecs.de
Mon Jan 12 09:42:57 PST 2009
I'm curious if RAID 1 (mirroring) really helps to protect data loss. Of
course if a whole disk "dies", RAID 1 has the advantage that
I have an identical copy. But what happens if only a sector of one disk
contains bad data. How can the RAID controller decide which is the
correct sector? Or would the disk detect such a case and return an error?
Instead of mirroring the disk on the block level, wouldn't a Hammer
mirror (to a second disk) provide the same degree of data protection?
Of course it wouldn't provide the automatic fail-over a RAID 1 setting
provides, and there would be no improvment for reading blocks, but on
the other hand it would stress the disk less, e.g. by mirroring only
every 5 minutes (don't know if that matters at all).
The background is, that I am planning to spend my old server (running
FreeBSD) a new huge disk and replace it with DragonFly :). The main
reason to use DragonFly for me is to ease backups, which right now is a
real pain (using rsync and hard-linking). ZFS would of course also
provide that, but I assume that Hammer runs better on a P4/i386 with not
too much memory.
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