Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Tue, May 21, 2013 at 11:52:58PM +0800, Mia Lueng wrote:
> I have 16G RAM in this server. Using a low dirty configuration may lead
> to a pool I/O performance?
Maybe this blog post, and the links referenced therein help?
https://blogs.linbit.com/p/548/umount-takes-time/
http://lists.linbit.com/pipermail/drbd-user/2012-September/019080.html
Lars
> 2013/5/14 Lars Ellenberg <lars.ellenberg at linbit.com>
>
> > On Thu, May 09, 2013 at 10:33:16AM +0800, Mia Lueng wrote:
> > > # sysctl -a|grep dirty
> > > vm.dirty_background_ratio = 10
> > > vm.dirty_background_bytes = 0
> > > vm.dirty_ratio = 20
> > > vm.dirty_bytes = 0
> > > vm.dirty_writeback_centisecs = 500
> > > vm.dirty_expire_centisecs = 3000
> > >
> > > bandwidth is 100M bps
> >
> > You can replicate around 10 to 12 MByte per second.
> > To avoid long "write-out stalls" when flushing caches,
> > you should not allow more than about 20 MByte dirty,
> > and start write out much earlier.
> >
> > vm.dirty_bytes=20100100
> > vm.dirty_background_bytes=500100
> > vm.dirty_writeback_centisecs=97
> >
> > A ratio of 20 % of available RAM may well mean several GB.
> > How much RAM do you have?
> >
> > Depending on what usage patterns and data characteristics
> > you actually have in production, maybe you want to try drbd-proxy.
> > Or check with LINBIT what other options you have.
> >
> > > 2013/5/9 Lars Ellenberg <lars.ellenberg at linbit.com>
> > >
> > > > On Thu, May 09, 2013 at 12:16:56AM +0800, Mia Lueng wrote:
> > > > > in drbd 8.4.3，I do the following test:
> > > > >
> > > > > [root at kvm3 drbd.d]# drbdadm dump drbd0
> > > > > # resource drbd0 on kvm3: not ignored, not stacked
> > > > > # defined at /etc/drbd.d/drbd0.res:1
> > > > > resource drbd0 {
> > > > > on kvm3 {
> > > > > device /dev/drbd0 minor 0;
> > > > > disk /dev/vg_kvm3/drbd0;
> > > > > meta-disk internal;
> > > > > address ipv4 192.168.10.6:7700;
> > > > > }
> > > > > on kvm4 {
> > > > > device /dev/drbd0 minor 0;
> > > > > disk /dev/vg_kvm4/drbd0;
> > > > > meta-disk internal;
> > > > > address ipv4 192.168.10.7:7700;
> > > > > }
> > > > > net {
> > > > > protocol A;
> > > > > csums-alg md5;
> > > > > verify-alg md5;
> > > > > ping-timeout 30;
> > > > > ping-int 30;
> > > > > max-epoch-size 8192;
> > > > > max-buffers 8912;
> > > > > unplug-watermark 131072;
> > > > > }
> > > > > disk {
> > > > > on-io-error pass_on;
> > > > > disk-barrier no;
> > > > > disk-flushes no;
> > > > > resync-rate 100M;
> > > > > c-plan-ahead 20;
> > > > > c-delay-target 100;
> > > > > c-max-rate 400M;
> > > > > c-min-rate 2M;
> > > > > al-extents 601;
> > > > > }
> > > > > }
> > > > >
> > > > > [root at kvm3 oradata]# dd if=t1 of=t2 bs=1M
> > > > > 5585+1 records in
> > > > > 5585+1 records out
> > > > > 5856305152 bytes (5.9 GB) copied, 286.119 s, 20.5 MB/s
> > > >
> > > > That writes to the page cache, and from there to the block device.
> > > >
> > > > No fsync, no sync: there will still be a few GB in the cache (RAM
> > only).
> > > >
> > > > > [root at kvm3 oradata]# cd
> > > > > [root at kvm3 ~]# umount /oradata
> > > > >
> > > > >
> > > > > it takes lots of time(up to 600 seconds) to umount the drbd mount
> > point.
> > > >
> > > > On umount, the filesystem obviously has to flush all dirty pages first.
> > > >
> > > > What is your replication bandwidth?
> > > >
> > > > > echo "1" >/proc/sys/vm/block_dump
> > > > > show when umount ,
> > > > >
> > > > > [root at kvm3 ~]# dmesg|tail -n 100
> > > > ...
> > > > > umount(3958): WRITE block 100925440 on dm-5
> > > > > umount(3958): WRITE block 100925440 on dm-5
> > > > > umount(3958): WRITE block 100925440 on dm-5
> > > > > umount(3958): WRITE block 0 on dm-5
> > > > > umount(3958): dirtied inode 1053911 (mtab.tmp) on dm-0
> > > > > umount(3958): dirtied inode 1053911 (mtab.tmp) on dm-0
> > > > > umount(3958): WRITE block 33845632 on dm-0
> > > > > umount(3958): dirtied inode 1053912 (?) on dm-0
> > > > >
> > > > >
> > > > > Is the reason that I use protocol A?
> > > >
> > > > No.
> > > >
> > > > But that you need to understand caching, and tunables.
> > > >
> > > > Some hints and keywords for a followup search:
> > > >
> > > > Check how much "dirty" data (writes not yet on stable storage)
> > > > is still in RAM:
> > > > grep Dirty /proc/meminfo
> > > >
> > > > Tune how much dirty data is "allowed"
> > > > sysctl
> > > > vm.dirty_background_bytes
> > > > vm.dirty_bytes
> > > > vm.dirty_writeback_centisecs
> > > > vm.dirty_expire_centisecs
> > > >
> > > > also compare:
> > > > time dd if=t1 of=t2 bs=1M; time sync
> > > > time dd if=t1 of=t2 bs=1M conv=fsync
--
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com
DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.
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