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

On 07/05/13 16:41, Jan-Aage Frydenbø-Bruvoll wrote:
> Hi,
>> Reason I ask is that with a single Windows 2008 R2 VM on XCP 1.6 all loaded 
>> on
>> a Samsung 840 500GB SSD I am getting IOPS and transfer rates in IOMeter that
>> are a fraction (as in 5%) of the manufacturers claims.
> Quite interested to hear your conclusions if any. We ended up dropping XCP as 
> a platform with the last bunch of VMs being replaced last Christmas, due to 
> IO and networking performance issues. We were never able to get more than 20 
> MBps out of the VM disks, and network performance was poor enough for it to 
> be impossible to run heavily loaded load balancers (IPVS) on them.
> I am sure our problems were due to configuration mistakes, at least I hope 
> so, but we have never seen anything like it in our new environment (on the 
> same hardware).
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.

I don't have the bug details on hand right now, but if you are
interested and can't find it, let me know and I'll dig it up.


Adam Goryachev
Website Managers

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