[rhelv6-list] Home-brew SAN for virtualization

[Chris Adams]

I have taken over a set of Xen servers somebody else built, and am now
rebuilding the CentOS-based storage (Dell MD3000 SAS storage shelf
connected to a couple of CentOS servers), and could use some advice.

The Xen servers are just "plain" Xen, with no clustering, and right now
all the VM images are local to each server (a mix of file-based raw
images and LVM logical volumes).  We'd like to get the storage rebuilt
to host the VM images on shared storage (initially to free up local
space for only higher-I/O stuff like mail queues, and eventually to
convert the whole thing to oVirt or some other clustered VM solution).

The storage was previously set up running NFS to share out all the
space, with some VMs running from raw file images over NFS.  That seems
somewhat inefficient to me, so I was considering setting up the rebuilt
storage with iSCSI for the VM storage, but then how do I manage it?  Do
people create a new LUN for each VM?  We have around 75 VMs right now.

Also, I was also considering using LVM thin provisioning, but a quick
test (under Fedora 20) seemed to show a high overhead for that; I/O
throughput dropped by about 50% compared to a "normal" logical volume
(created an LV+ext4, ran bonnie++, created an LV-pool+thin-LV+ext4, ran
bonnie++ a couple of times).  Is that expected?

-- 
Chris Adams <linux at cmadams.net>