Re: [Xen-users] anyone using dm-cache?

[Florian Heigl <florian.heigl@xxxxxxxxx>]

Hi,

2011/6/24 Rudi Ahlers <Rudi@xxxxxxxxxxx>:
> I'm looking for a way to speed up SAN based storage on a CentOS 5.6 + XEN
> Hypervisor which uses iSCSI mounted SAN storage. dm-cache seems like it do


I think the "write-through-write-around" (wt) version of flashcache[*]
might be better for the SSD caching use case.
I haven't tried it but you just basically made me stumble over it and
it seems the right thing for a Xen host. There's also documentation on
using it with Centos5.4 - good enough? :)

A write-back cache is also possible (and there's more work ongoing to
add something like that to linux) but I think a busy VM host will eat
through a SSD in too short time if we're caching writes.

I want to use that on my hosts since they only have 8 disks slots (so
6 normal 10k/15k disks on raid controller & 1 ssd & tbd).With a "real"
SAN I'd just trust in a reasonable number of raid10 spindles though -
SAN storage should be faster, not slower than local disks :>

> Does anyone use it?
> Any feedback? Pitfalls? Success stories?
As to actual _use_ i noted XCP 1.0 has "local storage caching" but
there is no documentation what makes up that feature.


[*] https://github.com/facebook/flashcache


Regards,
Florian

-- 
the purpose of libvirt is to provide an abstraction layer hiding all
xen features added since 2006 until they were finally understood and
copied by the kvm devs.

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