Not really, RAID6+0 only requires 8 drives minimum you can create two
RAID6's of 4 drives each and stripe them together. This has a benefit
as multi-layer based parity raids increases random write iops
performance. But the main issue is array integrity, mainly with
large capacity drives as they have UBR rates in 10^14 or 10^15 range but
when you consider their capacity this dominates availability
calculations for an array well over any 'hard' failure calculations.
Generally with 1TB+ drives with 10^14 UBR rates I would be hard pressed
to use more than 6 drives in a raid group (4D+2P), with 10^15 you may
get by with 8D+2P but you have to choose your own risk level.
Personally, I don't like building arrays that have a probability of not
reading a sector in a single sub array greater than 5% (ideally it
should be less than 1% but you're not going to get that unless you're
talking 10^16 and small drives (<500GB).
This still doesn't address the silent errors that happen which is the
main thrust behind file systems like ZFS and/or T10 DIF (fat sectors)
which do checking to make sure what sector your requesting is the sector
you're getting.
On 2011-03-18 08:22, Alan Brown wrote:
Phil Stracchino wrote:
With RAID6, you can survive any one or two disk failures, in degraded
mode. You'll have a larger working set than RAID10, but performance
will be slower because of the overhead of parity calculations. A third
failure will bring the array down and you will lose the data.
There's always RAID60, but that requires a lot of drives.
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