Verifying TRIM support on SSDs when using BtrFS
(resend with linux-btrfs Cced)
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Hi All,
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My company is considering using BtrFS for some of our production systems, but before we can use it, I must positively verify that the TRIM command is being issued to the SSDs. =E7=87=9F attempted to veri=
fy TRIM
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first using examples that work for Ext4
<http://andyduffell.com/techblog/?p=3D852>, but I had to make changes=
to
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the procedure to work with BtrFS.
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The server is Ubuntu 11.04 server 64-bit release (mkfs.btrfs version 0.19). I have installed the Linux 3.0.0 kernel as the BtrFS changelog states that bulk TRIM is not available in the kernel shipped with
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Ubuntu 11.04 (2.6.38).
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My testing methodology:
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* Manually TRIM the disks before starting: for i in {0..10} ; do let A=3D"$i * 65536" ; hdparm --trim-sector-ranges $A:65535 --please-destroy-my-drive/dev/sda; done
* Verify the drive was TRIM'd: ./sectors.pl |grep + | tee sectors-$(d=
ate +%s)
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* Partition the drive: fdisk
/dev/sda
* Make the file system: mkfs.btrfs/dev/sda1
* Mount: sudo mount -t btrfs -o ssd/dev/sda1/mnt
* Create a file: dd if=3D/dev/urandom of=3D/mnt/testfile bs=3D1k coun=
t=3D50000
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oflag=3Ddirect
* Verify the file is on the disk: ./sectors.pl | tee sectors-$(date +=
%s)
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* Delete the test file: rm
/mnt/testfile
* See that the test file is TRIM'd from the disk: ./sectors.pl | tee sectors-$(date +%s)
* Verify the TRIM'd blocks: diff the two most recent sectors-* files =20
At this point, the pre-delete and post delete verifications still sho=
w
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the same disk blocks in use. I should instead see a reduction in the number of in use blocks. Waiting an hour (in case it takes a while fo=
r
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the TRIM command to be issued) after the test file is deleted still shows the same blocks in use.
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I have also tried mounting with the "-o ssd,discard" options, but tha=
t
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doesn't seem to help at all.
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I also posted this question at
<http://serverfault.com/questions/307397/verify-trim-support-with-btr=
fs-on-ssd>
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but a good answer has yet to surface. If you are interested, you can see my sectors.pl and a little more detail at that URL. =20
Is my testing methodology flawed? Am I missing something here? Thanks for your help.
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Have you tried to use this methodology to test ext4? So you can verify = if
it's flawed.
I used a much simpler way to test this, and I found btrfs works fine:
# mount -t btrfs -o discard /dev/sdc5 /mnt # dd if=3D/dev/urandom of=3D/mnt/tmp bs=3D1M count=3D5 # sync # hexdump /mnt/tmp 0000000 064c ded5 c386 4721 060c 13e8 b090 b4a0 ... # hexdump /dev/sdc5 | grep '064c ded5' 0c00000 064c ded5 c386 4721 060c 13e8 b090 b4a0
Now verify the discard feature:
# rm /mnt/tmp # sync # echo 3 > /proc/sys/vm/drop_caches # hexdump /dev/sdc5 | grep '064c ded5' (grep returns nothing, as expected)
So there's nothing wrong in btrfs.
Try the above test but without discard option, and you'll see the secto= rs
will not be zeroed.
--
Li Zefan
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