[dm-crypt] aes-xts-plain with aes_x86_64 makes my SSD 5x slower than my encrypted HD

André Gall dm-crypt at andregall.de
Mon Jul 23 19:27:47 CEST 2012


I remember a test which I conducted after I received my Intel SDD 510 
120 GB about 1 year ago. I don't remember all the details, but the 
essence was that write speed decreased dramatically if the write process 
wasn't aligned.

I did:
dd if=/dev/zero of=/dev/sda bs=4k
I got around 400 Mb/sec, which was expected. But when I did:

dd if=/dev/zero of=/dev/sda bs=5k
I got only around 40 Mb/sec

When you write in 5k blocks, the SSD has to do a lot of overhead because 
of the Read-Modify-Write operations. I guess this might also be the case 
if you write in 4k blocks, but don't align them to the SSD's "native" 
blocks. So I would check for any misalignment.

Regards,
André


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