kvm-virtualizationlvmssd
I have a Dell R610 with hardware:
I have installed Centos 6.6 on this server and configured:
I have some questions:
I think you're stuck doing what you've mentioned if you want to do it without taking the machine down.
Why not just give the virtual machines LUNs right off the SAN and manage the space there? This works better if you want to use features like live migration anyhow.
KVM is based on QEMU so all it's image format support comes from that project. Here's a good how-to resize the various formats that Qemu/KVM support. But the Qemu forum would be a good place to ask this question if you don't get any solid answers here.
Another option which may not be ideal is to use really large qcow2 or other sparse image format for the drives. So you could give each machine a small drive for the OS and a large sparse image for data under LVM. This would at least keep the number of virtual drives/images that you're having to manage. But this thin provisioning could be a problem though if you do this to 1000 machines and everyone takes you up on the free space that they see.
XEN I believe has the same limitations currently.
Well, doesn't the SSD choice depend a bit on your anticipated workload?
Really: Are SSD drives as reliable as mechanical drives (2013)?
But generically, you can attach just about anything to an LSI (Perc) controller and make it work. Should you? I mean, these are still consumer disks...
There's no TRIM support on the hardware RAID controller (it's not common). It's also not that important. You can just under-provision the drives. Create a Virtual Disk smaller than the capacity of the SSDs; e.g. don't allocation all of the space to the disks.
Best Answer
TRIM works at the filesystem level so as you're giving your KVM domains a raw block device then you need to enable TRIM from within the domain; your host can't know the domains filesystem utilisation without examining it. To enable this you need to ensure there's a
discard='unmap'attribute added to the disk definition in the XML for the domain, this is documented at https://libvirt.org/formatdomain.html#elementsDisks .Setting
issue_discards = 1in /etc/lvm/lvm.conf means that LVM will issue a TRIM to the underlying PV if any logical volume is reduced or deleted. It's not necessary for normal filesystem TRIM operations.To initiate the actual TRIM operations, it's generally advised to use the
fstrimutility rather than adding thediscardmount option. Run this periodically from cron or equivalent. Running it manually will also show you if you've actually got everything set up properly too.To monitor your SSD's I would assume the S.M.A.R.T. tools should suffice, have a look at the output of
smartctl -a /dev/sdX.Optimising generally involves making sure all of your partitions are aligned properly and the same as with normal disks; minimize your writes where necessary. Adding mount options such as
noatime,nodiratime, etc.