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Hi,

we seem to have mitigated the SSD issues in am4 for now.

Apparently both the Crucial M4 as well as the Micron M500 slow
down considerably when being filled to ~90% capacity (and having no
DISCARD/TRIM to top it off). This is a sharp contrast to the Intel 520s
in fra who hum happily along at ~90% capacity (also no DISCARD).

http://imgur.com/a/ZgAz0 illustrates the issues - sda being the Micron
M500 and sdb being the Crucial M4.


For the Micron the recovery procedure was as expected - issue a
BLKDISCARD to a sizeable part of the device and performance is back to
normal instantly.

The Crucial on the other hand has been quite a pain in the ass to
troubleshoot. If you issue a BLKDISCARD all subsequent IO times will be
in the second-ranges and apparently don't return back to normal. After
finding some hints online [1] I gave the drive some "me-time" (disabling
all IO for 30 minutes) and after that it's also back to normal.

Our Crucial drives were shipped with the 040H firmware - the only more
recent one is 070H [2] which doesn't seem to address the behaviour
we're seeing.

For now I can only recommend to leave sufficient slack space on those
SSDs (we chose ~25%) and if possible run with a DISCARD/TRIM enabled IO
stack - especially for the Crucial drives, which don't cope well with
bulk discard operations.


best,
Michael

[1] http://forums.macrumors.com/showpost.php?p=16795044&postcount=5
[2] http://www.crucial.com/firmware/m4/070H/Crucial_m4_Firmware_Update_070H.pdf