RAID6 r-m-w, op-journaled fs, SSDs

[Peter Grandi]

[ ... ]

>> * Can Linux MD do "abbreviated" read-modify-write RAID6
>> updates like for RAID5? [ ... ]

> No. (patches welcome).

Ahhhm, but let me dig a bit deeper, even if it may be implied in
the answer: would it be *possible*?

That is, is the double parity scheme used in MS such that it is
possible to "subtract" the old content of a page and "add" the
new content of that page to both parity pages?

[ ... ]

> The ideal config for a journalled filesystem is for put the
> journal on a separate smaller lower-latency device.  e.g. a
> small RAID1 pair.

> In a previous work place I had good results with:
>   RAID1 pair of small disks with root, swap, journal
>   Large RAID5/6 array with bulk of filesystem.

Sound reasonable, except that I am allergic to RAID5 (except in
two cases) and RAID6 (in general). :-), but would work equally
well I guess with RAID10 and its delightful MD implementation.

[ ... ]

Thanks for the information!