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Date: Wed, 09 Nov 2011 19:14:40 +0100
From: Alexander Koch <mail@alexanderkoch.net>
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Subject: [dm-crypt] Testing TRIM with hdparm on dm-crypt
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To: dm-crypt@saout.de

Hello everyone,

I'm trying to verify that TRIM is actually working on my dm-crypt (LUKS) 
encrypted LVM volume with the following layers:

   SSD (Crucial M4 128GB) -> LVM -> LUKS -> ext4

I followed the guide available at [1], which includes these steps:

  1) create a random-filled file, sync to disk
  2) fetch LBAs via 'hdparm --fibmap'
  3) pick one sector, raw-read contents with 'hdparm --read-sector'
  4) delete the file, sync to disk
  5) re-read the sector chosen above, verify it contains zeroes

Unfortunately I already get a zeroed sector in step three:

 > $ hdparm --read-sector 271984 /dev/sdd
 >
 > /dev/sdd:
 > reading sector 271984: succeeded
 > 0000 0000 0000 0000 0000 0000 0000 0000
 > 0000 0000 0000 0000 0000 0000 0000 0000
 > 0000 0000 0000 0000 0000 0000 0000 0000
 > 0000 0000 0000 0000 0000 0000 0000 0000
 > (...)


Is there any LBA-calculation I must do because of the LVM layer?


Regards,

lynix



[1] 
http://techgage.com/article/enabling_and_testing_ssd_trim_support_under_linux/2