Mike Gerdts wrote:
On 6/17/06, Dale Ghent <[EMAIL PROTECTED]> wrote:
The concept of shifting blocks in a zpool around in the background as
part of a scrubbing process and/or on the order of a explicit command
to populate newly added devices seems like it could be right up ZFS's
alley. Perhaps it could also be done with volume-level granularity.
Off the top of my head, an area where this would be useful is
performance management - e.g. relieving load on a particular FC
interconnect or an overburdened RAID array controller/cache thus
allowing total no-downtime-to-cp-data-around flexibility when one is
horizontally scaling storage performance.
Another good use would be to migrate blocks that are rarely accessed
to slow storage (750 GB drives with RAID-Z) while very active blocks
are kept on fast storage (solid state disk). Presumably writes would
go to relatively fast storage and use idle IO cycles to migrate those
that don't have "a lot" of reads to slower storage. Blocks that are
very active and reside on slow storage could be migrated (mirrored?)
to fast storage.
Solid state disk often has a higher failure rate than normal disk and a
limited write cycle. Hence it is often desirable to try and redesign the
filesystem to do fewer writes when it is on (for example) compact flash,
so moving "hot blocks" to fast storage can have consequences.
But then there is also this new storage paradigm in the e-rags where
a hard drive also has some amount of solid state storage to speed up
the boot time. It'll be interesting to see how that plays out, but I
suspect the idea is that in the relevant market (PCs), it'll be used for
things like drivers and OS core image files that do not change very
often.
Darren
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