[CentOS] 40TB File System Recommendations

Tue Apr 12 13:56:52 UTC 2011
Rudi Ahlers <Rudi at SoftDux.com>

On Tue, Apr 12, 2011 at 3:48 PM, Markus Falb <markus.falb at fasel.at> wrote:

> On 12.4.2011 15:02, Marian Marinov wrote:
> > On Tuesday 12 April 2011 15:56:54
> rainer-RNrd0m5o0MABOiyIzIsiOw at public.gmane.org wrote:
> > Yes... but with such RAID10 solution you get only half of the disk
> space... so
> > from 10 2TB drives you get only 10TB instead of 16TB with RAID6.
> From a somewhat theoretical view, this is true for standard raid10 but
> Linux md raid10 is much more flexible as I understood it. You could do 2
> copys over 2 disks, thats like standard 10. Or you could do 2 copys over
> 2 or 3 or ... x disks. Or you could do 3 copys over 3 or 4 or ... x
> disks. Do the math. See the manpage for md(4) and
> http://en.wikipedia.org/wiki/Non-standard_RAID_levels#Linux_MD_RAID_10
> However, I have to admit that I have no experience with that but would
> like to hear about any disadvantages or if I am mislead. I am just
> interested.
> --

We only use RAID 10 (rather 1+0) and never even bothered with RAID6.  And
we've had no data loss in the past 3 years with it yet, on hundreds of

But, our RAID10 is setup as a stripe of mirrors, i.e. sda1 & sdb1 -> md0,
sdc1 + sdd1 ->md1, then sde1 + sdf1 ->md2, and finally md0 + md1 + md2 are
stripped. The advantage of this is that we can add more disks to the whole
RAID set with no downtime (all server have hot swap HDD cages) and very
little performance degradation since the 2 new drives  have to
be mirrored on their own first (take very little CPU / RAM resources) and
then added to the RAID set. Rebuild is generally quick since it only
rebuilds the broken mirror

Kind Regards
Rudi Ahlers

Website: http://www.SoftDux.com
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