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

Heinz Diehl htd at fancy-poultry.org
Tue Jul 24 16:27:53 CEST 2012

On 24.07.2012, Milan Broz wrote: 

> - Disable readahead
> # blockdev --setra 0 /dev/mapper/sdc_null_crypt 

This seems not only to be a problem with SSD drives, but also with
conventional harddisks. I've never seen something like this, because I
have had "blockdev --setra 8192 /dev/sda" in my rc.local for 
ages, because it's well known that it speeds up all disks significantly.

Here's a short test. The partition is encrypted with
256-bit twofish-xts-plain64:sha256.

[root at wildsau ~]# hdparm -i /dev/sda


 Model=Hitachi HTS723232L9A360, FwRev=FC4OC30F,
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4
 BuffType=DualPortCache, BuffSize=15058kB, MaxMultSect=16, MultSect=16
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=625142448
 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 pio3 pio4 
 DMA modes:  mdma0 mdma1 mdma2 
 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6 
 AdvancedPM=yes: mode=0x80 (128) WriteCache=enabled
 Drive conforms to: unknown:  ATA/ATAPI-2,3,4,5,6,7

With "blockdev --setra 8192" og "hdparm -tT":
Timing buffered disk reads: 234 MB in  3.01 seconds =  77.69 MB/sec

With "blockdev --setra 0" og "hdparm -tT":
Timing cached reads:   4670 MB in  2.00 seconds = 2336.29 MB/sec
Timing buffered disk reads:  14 MB in  3.06 seconds =   4.57 MB/sec

With "blockdev --setra 0" og "hdparm --direct -tT":
Timing O_DIRECT cached reads:   250 MB in  2.01 seconds = 124.45 MB/sec
Timing O_DIRECT disk reads: 238 MB in  3.02 seconds =  78.80 MB/sec

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