On 08/15/2009 11:39 AM, jim owens wrote:

***begin rant***

I have not seen any analysis of the benefit and cost to the
end user of the TRIM or array UNMAP. We now see that TRIM
as implemented by some (all?) SSDs will come at high cost.
The cost is all born by the host. Do we get any benefit, or
is it all for the device vendor. And when we subtract the cost
from the benefit, does the user actually benefit and how?

I'm tired of working around shit storage products and broken
device protocols from the "T" committees. I suggest we just
add a "white list" of devices that handle the discard fast
and without us needing NCQ queue drain. Then only send TRIM
to devices that are on the white list and throw the others
away in the block device layer.

They all will require NCQ queue drain. It's an inherent requirement of 
the protocol that you can't overlap NCQ and non-NCQ commands, and the 
trim command is not NCQ.

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