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Re: [Xen-users] SSD 4K Alignment?

On 08/05/13 00:01, Jan-Aage Frydenbø-Bruvoll wrote:
> Hi Adam,
>> Not sure exactly what Linux kernel version is used on XCP, or what disks/etc 
>> you were using,
>> but I can confirm that there was definitely a bug in Linux 2.6 from Debian 
>> Squeeze which seriously 
>> affected SSD performance (ie, reduced it to worse that HDD speed), which was 
>> fixed by upgrading
>> to debian squeeze backports kernel 3.0.0 I think from memory.
> Now that's interesting. The last kernel we tested on our XCP rig was 2.6.39, 
> which still had the problem. You wouldn't happen to have an idea whether the 
> same bug was present in other kernels as well?

Actually, it was in Linux mainline kernel, and had not been patched in
the latest Debian stable kernel (squeeze). I am positive it was fixed
before 3.0.0, and it might have been fixed by 2.6.39....

A very quick google search gives this:

>From there, you should be able to find when it was added/removed from
the kernel and whether the versions you used were affected or not.

PS, with my current Debian wheezy xen boxes, and my Debian squeeze iSCSI
server (with kernel and iscsi from backports), and 2 x 1G ethernet for
iSCSI on the xen boxes and 8 x 1G ethernet on the iSCSI box, I get
around 220MB/sec random read/write from the Windows 2003 domU.

PS, I'm using 5 x Intel 480GB SSD's in RAID5 on the iSCSI server, with
DRBD which replicates to a second iSCSI server. Using Intel dual port
(xen) and quad port (iSCSI) cards.

The iSCSI server gets around 1.6GB/s random write, and 2.6GB/s random
read... (read speed may be a bit wrong with my memory, but write speed
is correct because I know I can at least fill my 8 x 1Gbps ethernet if I
had 4 or more xen boxes hitting their disks hard).


Adam Goryachev
Website Managers
Ph: +61 2 8304 0000                            adam@xxxxxxxxxxxxxxxxxxxxxx
Fax: +61 2 8304 0001                            www.websitemanagers.com.au

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