Hi list,
I deployed a Windows 7 VM with qemu-rbd disk, and got an unexpected booting
phase performance.
I discovered that when booting the Windows VM up, there are consecutive ~2
minutes that `ceph -w` gives me an interesting log like: "... 567 KB/s rd,
567 op/s", "... 789 KB/s rd, 789 op/s" and so on.
e.g.
2014-06-05 15:47:43.125441 mon.0 [INF] pgmap v18095: 320 pgs: 320
active+clean; 86954 MB data, 190 GB used, 2603 GB / 2793 GB avail; 765 kB/s
rd, 765 op/s
2014-06-05 15:47:44.240662 mon.0 [INF] pgmap v18096: 320 pgs: 320
active+clean; 86954 MB data, 190 GB used, 2603 GB / 2793 GB avail; 568 kB/s
rd, 568 op/s
... (skipped)
2014-06-05 15:50:02.441523 mon.0 [INF] pgmap v18186: 320 pgs: 320
active+clean; 86954 MB data, 190 GB used, 2603 GB / 2793 GB avail; 412 kB/s
rd, 412 op/s
Which shows the number of rps is always the same as the number of ops, i.e.
every operation is nearly 1KB, and I think this leads a very long boot time
(takes 2 mins to enter desktop). But I can't understand why, is it an issue
of my Ceph cluster? Or just some special I/O patterns in Windows VM booting
process?
In addition, I know that there are no qemu-rbd caching benefits during boot
phase since the cache is not persistent (please corrects me), so is it
possible to enlarge the read_ahead size in qemu-rbd driver? And does this
make any sense?
And finally, how can I tune up my Ceph cluster for this workload (booting
Windows VM)?
Any advice and suggestions will be greatly appreciated.
Context:
4 OSDs (7200rpm/750GB/SATA) with replication factor 2.
The system disk in Windows VM is NTFS formatted with default 4K block size.
$ uname -a
Linux ceph-consumer 3.11.0-22-generic #38~precise1-Ubuntu SMP Fri May
16 20:47:57 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
$ ceph --version
ceph version 0.80.1 (a38fe1169b6d2ac98b427334c12d7cf81f809b74)
$ dpkg -l | grep rbd
ii librbd-dev 0.80.1-1precise
RADOS block device client library (development files)
ii librbd1 0.80.1-1precise
RADOS block device client library
$ virsh version
Compiled against library: libvir 0.9.8
Using library: libvir 0.9.8
Using API: QEMU 0.9.8
Running hypervisor: QEMU 1.7.1 ()
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