On 9/20/07, Roch - PAE <[EMAIL PROTECTED]> wrote:
>
> Next application modifies D0 -> D0' and also writes other
> data D3, D4. Now you have
>
> Disk0 Disk1 Disk2 Disk3
>
> D0 D1 D2 P0,1,2
> D0' D3 D4 P0',3,4
>
> But if D1 and D2 stays immutable for long time then we can
> run out of pool blocks with D0 held down in an half-freed state.
> So as we near full pool capacity, a scrubber would have to walk
> the stripes and look for partially freed ones. Then it
> would need to do a scrubbing "read/write" on D1, D2 so that
> they become part of a new stripe with some other data
> freeing the full initial stripe.
>
Or, given a list of partial stripes (and sufficient cache), next write
of D5 could be combined with D1,D2:
Disk0 Disk1 Disk2 Disk3
D0 D1 D2 P0,1,2
D0' D3 D4 P0',3,4
D5 free free P5,1,2
therefore freeing D0 and P012:
Disk0 Disk1 Disk2 Disk3
free D1 D2 free
D0' D3 D4 P0',3,4
D5 free free P5,1,2
(I assumed no need for alignment). Performance-wise, i'm guessing it
might be beneficial to "quickly" write mirrored blocks on the disk and
later combine them, freeing the now unneeded mirrors.
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