Re: [Xen-users] Cheap IOMMU hardware and ECC support importance

[Kuba <kuba.0000@xxxxx>]

W dniu 2014-06-28 09:45, lee pisze:

> > and your workload includes a lot of synchronous writes. But
> > for that workload you would probably be better off getting an
> > SSD and using ZFS with ZIL in terms of total cost, performance
> > and reliability.
> SSDs still loose badly when you compare price with capacity.  For what I
> payed for the RAID controller, I could now buy two 120GB SSDs (couldn't
> back then).  That means two disks more, requiring two more SATA ports
> (11 in total), and an increased overall chance of disk failures because
> the more disks you have, the more can fail.
>
> I don't know about ZFS, though, never used that.  How much CPU overhead
> is involved with that?  I don't need any more CPU overhead like comes
> with software raid.
ZFS offers you two things RAID controller AFAIK cannot do for you: 
end-to-end data checksumming and SSD caching. If anything happens with 
your data on its round trip from the CPU to the disk and back, ZFS will 
detect that and, provided you have some redundancy, will correct it. 
That feature alone, IMHO, makes reading about ZFS worthwhile. As Gordan 
states, ZFS can also cache your data using a small SSD. Oversimplifying, 
the size of the SSD might be around the size of your data set.
Moreover, it blends in with xen quite nicely, e.g. using ZFS ZVOLs as 
block devices for domUs makes cloning and snapshotting easy (and that's 
just for starters).
Kuba


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