"Robert Wessel" wrote in message
om...

....

While that neatly avoids much of the work in the RAID10-RAID5
conversion, Aren't you screwed when you need to go the other way?
Unless you save that for a out-of-line process as well, presumably
driven by some accumulated usage statistics (stripe X gets heavy
updates, migrate it to RAID10).

My (now somewhat vague) recollection is that they maintain usage stats on
the stripes - that's how they determine what to move to RAID-5 when space
starts to get tight. And there's at least somewhat less movement in the
reverse direction: typical usage tends to be create, use heavily, use
lightly, then delete (and for that matter update-in-place operations are
themselves usually the exception rather than the rule, so perhaps the *most*
typical usage - save for actively-updated databases - is create, then read
one or more times, then delete).


Stripe level HSM, IOW?

Yup.

- bill