[Gluster-users] Performance

[Joe Landman]

On 04/20/2011 07:28 PM, Mohit Anchlia wrote:
> dd of=/dev/null if=/dev/sda bs=128k count=80k iflag=direct
> 81920+0 records in
> 81920+0 records out
> 10737418240 bytes (11 GB) copied, 83.8293 seconds, 128 MB/s

Ok, this is closer to what I was expecting (really ~150 MB/s would make 
more sense to me, but I can live with 128 MB/s).

The write speed is definitely problematic.  I am wondering if write 
cache is off, and other features are turned off in strange ways.

This is a 2 year old SATA disk

[root at smash ~]# dd if=/dev/zero of=/dev/sda2 bs=128k oflag=direct
dd: writing `/dev/sda2': No space left on device
16379+0 records in
16378+0 records out
2146798080 bytes (2.1 GB) copied, 20.8322 s, 103 MB/s

Write cache is enabled.  Turning write cache off (might not be so 
relevant for a RAID0),

[root at smash ~]# hdparm -W /dev/sda

/dev/sda:
  write-caching =  1 (on)
[root at smash ~]# hdparm -W0 /dev/sda

/dev/sda:
  setting drive write-caching to 0 (off)
  write-caching =  0 (off)

[root at smash ~]# dd if=/dev/zero of=/dev/sda2 bs=128k oflag=direct
dd: writing `/dev/sda2': No space left on device
16379+0 records in
16378+0 records out
2146798080 bytes (2.1 GB) copied, 155.636 s, 13.8 MB/s

See if you can do an

	hdparm -W1 /dev/sda

and see if it has any impact on the write speed.  If you are using a 
RAID0, safety isn't so much on your mind anyway, so you can see if you 
can adjust your cache settings.  If this doesn't work, you might need to 
get to the console and tell it to allow caching.


-- 
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics, Inc.
email: landman at scalableinformatics.com
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