Weird read performance

Printable View

11-27-2010, 07:49 PM
andreasg

Weird read performance

I have got a SAN with 13 Sata-HDDs bound to a Server with 4 x 1Gbit NICs with MPIO.

Read throughput is arround 110-120MB/s (all NICs get used)
Write throughput is at more than 300MB/s

Can someone give me a hint?

BTW: Server OS: RHEL6 or Debian Lenny both open-iscsi initiator.

Thanks in advance

Andreas Grabner
11-28-2010, 04:36 PM
To-M

Does the RAID Controller have the Read Cache enabled? Also if you are not using the volume replication try to enable the Write Back cache on the LUN by selecting the "WB" option.
11-29-2010, 08:58 AM
andreasg

Quote:

Originally Posted by To-M

Does the RAID Controller have the Read Cache enabled? Also if you are not using the volume replication try to enable the Write Back cache on the LUN by selecting the "WB" option.

The following settings are active:
ARECA RAID6:
Volume Data Read Ahead: Normal
HDD Read Ahead Cache: Enabled

WB (Write Back?) needs to be disabled because of planed replication.
Writeperformance is more than 350MB/s ??

I will open a Ticket via eurostor later this day.

Andreas Grabner
09-22-2011, 05:10 AM
dwright1542

Resolved?

Quote:

Originally Posted by andreasg

The following settings are active:
ARECA RAID6:
Volume Data Read Ahead: Normal
HDD Read Ahead Cache: Enabled

WB (Write Back?) needs to be disabled because of planed replication.
Writeperformance is more than 350MB/s ??

I will open a Ticket via eurostor later this day.

Andreas Grabner

Was this ever resolved? I'm seeing the exact same thing on my DSS V6
10-10-2011, 04:54 PM
marcinrozanski

99.9 of the time it's the RAID controllers cache settings

Please check this post - http://kb.open-e.com/System-performa...ings_1283.html

Cache setting can be changed "on-the-fly" without any risk to your data only the stripe-size change means re-RAIDing. Please get yourself a BBU for RAID card and UPS.

And remember those three simple rules of IT:

0 - do backups
1 - do backups
2 - do backups