On 2013-11-07 17:47, Gruher, Joseph R wrote:
I wonder how effective trim would be on a Ceph journal area.
If the journal empties and is then trimmed the next write cycle
should
be faster, but if the journal is active all the time the benefits
would be lost almost immediately, as those cells are going to receive
data again almost immediately and go back to an "untrimmed" state
until the next trim occurs.
If it's under-provisioned (so the device knows there are unused cells),
the device would simply write to an empty cell and flag the old cell for
erasing, so there should be no change. Latency would rise when
sustained write rate exceeded the devices' ability to clear cells, so
eventually the stock of ready cells would be depleted.
FWIW, I think there is considerable mileage in the larger-consumer
grade argument. Assuming drives will be half the price in a years time,
so selecting devices that can last only a year is preferable to spending
3x the price on one that can survive three. That though opens the tin
of worms that is SMART reporting and moving journals at some future
point mind.
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