[dm-crypt] FSB saturation?

Kyle Rose krose at krose.org
Sat May 14 17:35:05 CEST 2011


Nope. :-)

root at yupa:~# dd if=/dev/md1 of=/dev/null bs=64k count=65536
65536+0 records in
65536+0 records out
4294967296 bytes (4.3 GB) copied, 10.1625 s, 423 MB/s
root at yupa:~# dd if=/dev/mapper/yupa of=/dev/null bs=64k count=65536
65536+0 records in
65536+0 records out
4294967296 bytes (4.3 GB) copied, 35.2504 s, 122 MB/s


On Sat, May 14, 2011 at 11:30 AM, Milan Broz <mbroz at redhat.com> wrote:
> On 05/14/2011 04:36 PM, Kyle Rose wrote:
>> For the past week I've been trying to figure out why my
>> dm-crypt-on-RAID6 performance is so terrible. To wit:
>>
>> root at yupa:/source# hdparm -t /dev/md1
>>
>> /dev/md1: <---the RAID 6 block device
>>  Timing buffered disk reads: 1262 MB in  3.00 seconds = 420.19 MB/sec
>>
>> root at yupa:/source# hdparm -t /dev/mapper/yupa
>>
>> /dev/mapper/yupa: <---the dm-crypt device with /dev/md1 as the underlying store
>>  Timing buffered disk reads: 370 MB in  3.00 seconds = 123.26 MB/sec
>
> IIRC hdparm is doing direct io of size 2MB.
>
> Can you try do the same but with dd (just dd from device without direct mode).
> like "dd if=/dev/md1 of=/dev/null bs=64k count=4096"
>
> Gives it better throughput now? (on 2.6.38 and above)
>
> Milan
>


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