[DRBD-user] Slow Reads on VM - Xenserver and DRBD

Christian Balzer chibi at gol.com
Wed Jul 25 02:56:46 CEST 2012

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


On Tue, 24 Jul 2012 14:08:29 +0200 Phil Stricker wrote:

> Hi!
> 
> One Problem is solved:
> The extremely bad read-performance in the VM is gone away after the
> downgrade from DRBD 8.4.1 to 8.3.13!!
> 
Ah yes, 8.4... ^o^

 
> There is just one problem left:
> The setup "xenserver <-> LSI9260 <-> 8x SSD" is too slow! I can just get
> about 450 MB/s - no matter, if i set it up as an Raid 10 or Raid 0!
>
This is xenserver directly talking to the RAID device, not DRBD?
 
> Did you ever see something like that?
Not using xenserver, but that now really looks like a xenserver limitation.

This is what I get on an Adaptec 51645 with an 8 disk RAID10 of 2TB SATA
Hitachi drives (bonnie++):
---
 3.2, 8disk R10, ext4, 1G journal
Version  1.96       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
mb13            64G           529030  55 270813  33           1072430  63 642.0  50
---

So the writes on this setup with inferior drives are faster than your reads
and reads are twice as fast...

Regards,

Christian
-- 
Christian Balzer        Network/Systems Engineer                
chibi at gol.com   	Global OnLine Japan/Fusion Communications
http://www.gol.com/



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