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Discussing the differences between using a 2 member RAID1 where one
device is periodically removed and rotated offsite to a 3 member RAID1
where one device is periodically removed and rotated offsite.
On 27/04/11 22:47, Jeffrey J. Kosowsky wrote:
> I still think that losing all 3 (which however unlikely is still
> possible) is way, way, way, worse than potentially losing 1-2 out of 3
> and still having a spare to recover (carefully) from. And my case can
> occur if you lose a disk controller or if there is a transient or if
> you do something stupid and overwrite the disk, etc...
I'm not sure why you think you would lose 3 out of 3? Sure, with the 3
member RAID1 setup, you need one additional drive compared to your 2
device RAID1 setup.
ie, 2 RAID1 devices are always installed, another 3 devices are rotated,
with one offsite, one onsite, and the third in one of (transit, offsite,
onsite). Thus, if your 'worst case' of the three member RAID1 going bad,
then you still have the device you just failed out of the RAID1, as well
as the final offsite RAID1 member. Thus you need to lose both RAID1
devices during a resync before you need to rely on the device you just
removed, or finally the offsite copy.
Alternatively, with a max 2 member RAID1 device, you only need to lose
one drive during a resync to have the same result.
BTW interface failure, controller failure, etc are all of equal risk in
either case, so IMHO, that can be ignored as far as determining the
cost/benefit of these two particular cases (but of course, should also
be considered somewhere else).
Regards,
Adam
- --
Adam Goryachev
Website Managers
www.websitemanagers.com.au
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