Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Hey all,
I've got several DRBD resources, residing on top of LVM LV's:
[root at xen-ha-f1:~]# uname -a
Linux xen-ha-f1.unet.brandeis.edu 2.6.18.8-64bit-3-xen0 #1 SMP Tue Jul
21 16:38:41 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux
[root at xen-ha-f1:~]# cat /etc/redhat-release
Red Hat Enterprise Linux Server release 5.3 (Tikanga)
[root at xen-ha-f1:~]# rpm -q --qf='%{Version}' xen
3.4.1rc8
[root at xen-ha-g1:~]# vgs
VG #PV #LV #SN Attr VSize VFree
vg0 1 3 0 wz--n- 390.12G 283.12G
[root at xen-ha-g1:~]# lvs
LV VG Attr LSize Origin Snap% Move Log
Copy% Convert
drbd-bigtest vg0 -wi-ao
100.00G
drbd-vm_ha-test1 vg0 -wi-ao
6.00G
drbd-vm_ha-test1_swap vg0 -wi-ao
1.00G
[root at xen-ha-g1:~]# drbd-overview
0:vm_ha-test1 Connected Primary/Primary UpToDate/UpToDate C r----
1:vm_ha-test1_swap Connected Primary/Primary UpToDate/UpToDate C r----
2:bigtest Connected Secondary/Primary UpToDate/UpToDate C r----
There is only one physical volume (PV) for the above volume group (vg0):
/dev/md6... which is a RAID-1 set of two partitions on Seagate SAS
15krpm drives. There is a SAS controller card; no hardware RAID or any
battery-backed cache. This setup consists of two Dell PowerEdge 1950 III's.
Enough background information and onto the question...
The drbd.conf manpage states that DRBD will automatically choose the
first write-after-write method available supported by the backing
storage device, but it also states LVM does not support barriers.
However... it looks like DRBD is indeed choosing the barriers method, as
I have "wo:b" in /proc/drbd for all three resources.
Should I be forcing DRBD to use the flush method instead? By specifying
no-disk-barrier? Or should I actually be using the barrier method,
instead of flush? And what are the differences between the barriers and
flush methods?
If you need any further information just let me know.
Thanks.
--
Joshua West
Senior Systems Engineer
Brandeis University
http://www.brandeis.edu