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@wildsau ~]# hdparm -i /dev/sda
/dev/sda:
Model=Hitachi HTS723232L9A360, FwRev=FC4OC30F,
SerialNo=090119FC1400NEGNHSTD
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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