Dear Pranith /Anand , Update on our progress with using KVM & Gluster: We built a two server (Dell R710) cluster, each box has... 5 x 500 GB SATA RAID5 array (software raid) an Intel 10GB ethernet HBA. One box has 8GB RAM, the other 48GB both have 2 x E5520 Xeon Centos 6.3 installed Gluster 3.3 installed from the rpm files on the gluster site 1) create a replicated gluster volume (on top of xfs) 2) setup qemu/kvm with a gluster volume (mounts localhost:/gluster-vol) 3) sanlock configured (this is evil!) 4) build a virtual machines with 30GB qcow2 image, 1GB RAM 5) clone this VM into 4 machines 6) check that live migration works (OK) Start basic test cycle: a) migrate all machines to host #1, then reboot host #2 b) watch logs for self-heal to complete c) migrate VM's to host #2, reboot host #1 d) check logs for self heal The above cycle can be repeated numerous times, and completes without error, provided that no (or little) load is on the VM. If I give the VM's a work load, such by running "bonnie++" on each VM, things start to break. 1) it becomes almost impossible to log in to each VM 2) the kernel on each VM starts giving timeout errors i.e. "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" 3) top / uptime on the hosts shows load average of up to 24 4) dd write speed (block size 1K) to gluster is around 3MB/s on the host While I agree that running bonnie++ on four VM's is possibly unfair, there are load spikes on quiet machines (yum updates etc). I suspect that the I/O of one VM starts blocking that of another VM, and the pressure builds up rapidly on gluster - which does not seem to cope well under pressure. Possibly this is the access pattern / block size of qcow2 disks? I'm (slightly) disappointed. Though it doesn't corrupt data, the I/O performance is < 1% of my hardwares capability. Hopefully work on buffering and other tuning will fix this ? Or maybe the work mentioned getting qemu talking directly to gluster will fix this? best wishes Jake -- Dr Jake Grimmett Head Of Scientific Computing MRC Laboratory of Molecular Biology Hills Road, Cambridge, CB2 0QH, UK. Phone 01223 402219 Mobile 0776 9886539
