[plug] Cheap iSCSI .vs. NFS for VM's

William Kenworthy billk at iinet.net.au
Thu Jan 24 02:43:01 UTC 2013

I am using "ceph" - well putting a ceph/libvirsh setup in place.  Anyone
else playing with "ceph"?


On 24/01/13 08:34, Leon Wright wrote:
> Tim,
> We're using NFS off our NetApp boxes, hooked up to ESXi. Everything is
> thin provisioned, but we still used cooked file systems (vmdks). As
> we've yet to get better performance by direct NFS mounting to the filer
> inside the VM. We haven't finished testing that though as most of the
> VMs were migrated off old iSCSI fibre channel sans. The NetApps also
> dedup, so inefficient space usage isn't so much of an issue for us.
> Regards,
> Leon
> --
> DRM 'manages access' in the same way that jail 'manages freedom.'
> # cat /dev/mem | strings | grep -i cats
> Damn, my RAM is full of cats... MEOW!!
> On Thu, Jan 24, 2013 at 4:58 AM, Tim White <weirdit at gmail.com
> <mailto:weirdit at gmail.com>> wrote:
>     I've been doing lots of research recently into iSCSI .vs. NFS for
>     our virtual machines at work. I now have a preference based on my
>     research, but am wondering if I've missed anything that others can
>     point out for me, based on their industry experience.
>     At work we are using QNAP 6 bay NAS, currently in RAID6 but aiming
>     to migrate to RAID10 eventually. We have 2 Virtual Hosts connected
>     via a dedicated storage network. We'll also be adding another NAS in
>     the near future, possibly a QNAP as well.
>     Our current setup is with ESXi and iSCSI. However I'm migrating to
>     Proxmox (KVM) and so have the option to migrate to NFS at that point.
>     Currently, iSCSI is thick provisioned, and then the VM HDD is thin
>     provisioned in that iSCSI. This means we can never "over subscribe"
>     our storage. However it also means we are using all the disk space
>     in the QNAP even though we've actually only used 2/3 of that (or
>     less). I know that iSCSI can be thin provisioned, so this is a moot
>     point.
>     iSCSI and ESXi (on QNAP, I assume higher end systems do it
>     differently) is essentially a file system within a file system
>     within a filesystem. You have the QNAP filesystem, which you then
>     create a sparse file in, (iSCSI backing), which you then export via
>     iSCSI and create a filesystem in (VMFS) which is then filled with
>     your disk images (VMDK) which is then shown to the guest who then
>     creates another filesystem in. With Proxmox you can reduce this by
>     using it as LVM with iSCSI backing, but then you don't get all the
>     qcow features (although LVM is pretty good).
>     To me, a qcow on NFS seems like the least "filesystem within
>     filesystem" that you can get.
>     NFS .vs. iSCSI speed? Apparently without offloader devices, they are
>     basically the same now days.
>     Handling of network issues. Apparently iSCSI does this better than
>     NFS, but if we have a network issue on the storage network, I
>     believe it's going to cause problems regardless of protocol.
>     From everything I've been reading, I struggle to see why iSCSI is
>     used to much. I can see if the iSCSI is exporting a raw raid array
>     for example, (no filesystem), then the filesystem within a
>     filesystem issue is not really there. But on low end NAS's it seems
>     to me that NFS is just as good. And I don't have to worry about
>     iSCSI provisioning, I just create the qcow's as needed, and manage
>     the free space so that a sudden spike in usage doesn't crash a VM
>     (which will happen regardless of protocol as discovered by one of
>     the iSCSI lun's being provisioned slightly smaller than the disk
>     inside it by the previous network manager).
>     So for all those out in the industry, what do you use, and why? How
>     does iSCSI make your life better, or is it a left over from when
>     it's performance was better than NFS?
>     Thanks
>     Tim
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