SATA controllers

[Tom H]

>>> I'm speccing a new machine and as part of it I'd like to have a
>>> linux-controlled 4-disk RAID 6 array using SATA 3 Gbps disks (aka STA 2).

>> You want more than 4 disks for RAID6. Seriously.

>> RAID6 uses 2 parity drives; this means you get the capacity of (N-2)
>> drives, where N is the number of drives. Ergo, use 4 drives, you only
>> get the capacity of 2. This is pointless, because if you lose half the
>> capacity, you would get /much/ better performance from RAID10 (a
>> mirror of stripes) or RAID 0+1 (a stripe set of mirror pairs).

> md raid10 != md raid1+0. You can do a lot of fancy configs with the
> raid10 module that is not quite the same as nested raid1+0. Anyway,
> raid6 can lose any two drives whereas raid1+0 allows you to lose a
> specific combination of two drive loss. So you choose between
> performance or higher chance of survival. Given that disks of the same
> batch can have the tendency of dying together it is a risk that is worth
> considering.

LOL. The whole non-single digit RAID business weird.

AFAIK, mdadm has a raid10 driver that basically results in what RAID
1+0 does without nesting... And IIRC, at one point, what we now call
1+0 was called 0+1!