Re: [Xen-users] Software Raid 5 domu performance drop

[James Harper <james.harper@xxxxxxxxxxxxxxxx>]

> 
> On 05/26/2013 02:39 PM, Micky wrote:
> > Software raids by design have huge performance hits.
> 
> Who told you that? The ARM ASIC on a typical RAID controller has a lot
> less throughput for XOR-ing data than the main CPU in the system, and
> also has a lot less RAM for caching. If anything software RAID is going
> to be faster if you are operating at saturation point.

What spoils it is that hardware raid normally has nv write cache which can be a 
huge boost for performance, especially for raid5. Bcache fixes that to some 
extent but I'm not aware of any cheap battery backed memory cards. SSD is the 
next best thing but that's often attached via SATA or SAS.

James

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