Hi,
Perhaps I am doing something stupid, but I would like to understand
why there is a difference in the following situation.
I have defined a stripe device thusly:
"echo 0 17560535040 striped 9 8 /dev/sdd 0 /dev/sde 0 /dev/sdf 0
/dev/sdg 0 /dev/sdh 0 /dev/sdi 0 /dev/sdj 0 /dev/sdk 0 /dev/sdl 0 |
dmsetup create stripe_dev"
Then is did the following:
dd if=/dev/zero of=/dev/mapper/stripe_dev bs=262144 count=1000000
and I got 880 MB/s
However, when I changed that command to:
dd if=/dev/zero of=/dev/mapper/stripe_dev bs=262144 count=1000000
oflag=direct
I get 210 MB/s reliably.
The system in question is a 16 core (probably two CPUs) Intel Xeon
E5620 @2.40Ghz with 64GB of memory and 12 7200PRM SATA drives
connected to an LSI SAS controller but set up as a JBOD of 12 drives.
Why do I see such a big performance difference? Does writing to the
device also use the page cache if I don't specify DIRECT IO?
--
Regards,
Richard Sharpe
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
