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Old 7th June 2012, 06:55 PM
greno Offline
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Join Date: Oct 2005
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Redux: F17 and Discard (TRIM) support on LUKS/dm-crypt devices

Refer to this archived thread for context: http://forums.fedoraforum.org/showthread.php?t=278455

I followed the configuration changes outlined in that thread in my F17 installation and it seems I may now have discard support on my luks partition which is on SSD.

# cryptsetup status luks-cc282d6b-3831-448d-afa8-a53b30ee98e6
/dev/mapper/luks-cc282d6b-3831-448d-afa8-a53b30ee98e6 is active and is in use.
  type:    LUKS1
  cipher:  aes-xts-plain64
  keysize: 512 bits
  device:  /dev/sda3
  offset:  4096 sectors
  size:    330133504 sectors
  mode:    read/write
  flags:   discards
So I tried manually running fstrim:
# time fstrim -v /
/: 132014465024 bytes were trimmed

real	2m39.631s
user	0m0.000s
sys	0m0.814s
Not sure I trust the number of bytes trimmed since its showing about 130G !!

So how do I perform an actual test that I can see the TRIM occur on the encrypted block device? eg: all zeroes

UPDATE: painstakingly I went and followed through all the offsets of all the layers and was able to read a file sector and determine that yes TRIM is working on my LUKS partition.

Hope we see a tool to do this at some point.


Last edited by greno; 8th June 2012 at 01:05 AM.
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