Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
They say that the original host does the caching.
In KVM it's easy to turndown the cache
I use libvirtd and qemu-kvm to start the vm's
see attachement.
On 31 mei 2012, at 08:07, Wiebe Cazemier wrote:
> Hi,
>
> How did you turn off the cache? And how much did that influence performance?
>
> I'll try, but I'd rather find a solution that doesn't involve turning off the cache.
>
> Wiebe
>
>
> From: "Marcel Kraan" <marcel at kraan.net>
> To: "Wiebe Cazemier" <wiebe at halfgaar.net>
> Cc: drbd-user at lists.linbit.com
> Sent: Thursday, 31 May, 2012 7:58:10 AM
> Subject: Re: [DRBD-user] Xen DomU on DRBD device: barrier errors
>
> Helllo Wiebe,
>
> I had that also.
> But when i turned down the cache on the storage, and the other vm clients the error was gone.
> So no cache on the VM's and it worked very good.
>
>
> marcel
>
>
> On 30 mei 2012, at 17:13, Wiebe Cazemier wrote:
>
> Hi,
>
> I'm testing setting up a Xen DomU with a DRBD storage for easy failover. Most of the time, immediately after booting the DomU, I get an IO error:
>
> [ 3.153370] EXT3-fs (xvda2): using internal journal
> [ 3.277115] ip_tables: (C) 2000-2006 Netfilter Core Team
> [ 3.336014] nf_conntrack version 0.5.0 (3899 buckets, 15596 max)
> [ 3.515604] init: failsafe main process (397) killed by TERM signal
> [ 3.801589] blkfront: barrier: write xvda2 op failed
> [ 3.801597] blkfront: xvda2: barrier or flush: disabled
> [ 3.801611] end_request: I/O error, dev xvda2, sector 52171168
> [ 3.801630] end_request: I/O error, dev xvda2, sector 52171168
> [ 3.801642] Buffer I/O error on device xvda2, logical block 6521396
> [ 3.801652] lost page write due to I/O error on xvda2
> [ 3.801755] Aborting journal on device xvda2.
> [ 3.804415] EXT3-fs (xvda2): error: ext3_journal_start_sb: Detected aborted journal
> [ 3.804434] EXT3-fs (xvda2): error: remounting filesystem read-only
> [ 3.814754] journal commit I/O error
> [ 6.973831] init: udev-fallback-graphics main process (538) terminated with status 1
> [ 6.992267] init: plymouth-splash main process (546) terminated with status 1
>
> The manpage of drbdsetup says that LVM (which I use) doesn't support barriers (better known as "tagged command queuing" or "native command queuing"), so I configured the DRBD device not to use barriers. This can be seen in /proc/drbd (by "wo:f, meaning flush, the next method drbd chooses after barrier):
>
> 3: cs:Connected ro:Primary/Secondary ds:UpToDate/UpToDate C r----
> ns:2160152 nr:520204 dw:2680344 dr:2678107 al:3549 bm:9183 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0
>
> And on the other host:
>
> 3: cs:Connected ro:Secondary/Primary ds:UpToDate/UpToDate C r----
> ns:0 nr:2160152 dw:2160152 dr:0 al:0 bm:8052 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0
>
> I also enabled the option disable_sendpage, as per the DRBD docs:
>
> cat /sys/module/drbd/parameters/disable_sendpage
> Y
>
> I also tried adding barriers=0 to fstab as mount option. Still it says:
>
> [ 58.603896] blkfront: barrier: write xvda2 op failed
> [ 58.603903] blkfront: xvda2: barrier or flush: disabled
>
> I don't even know if ext3 has a nobarrier option, but it does seem to work. But, because only one of my storage systems is battery backed, it would not be smart.
>
> Why does it still compain about barriers when I disabled that?
>
> Both hosts are:
>
> Debian: 6.0.4
> uname -a: Linux 2.6.32-5-xen-amd64
> drbd: 8.3.7
> Xen: 4.0.1
>
> Guest:
>
> Ubuntu 12.04 LTS
> uname -a: Linux 3.2.0-24-generic pvops
>
> drbd resource:
>
> resource drbdvm
> {
> meta-disk internal;
> device /dev/drbd3;
>
> startup
> {
> # The timeout value when the last known state of the other side was available. 0 means infinite.
> wfc-timeout 0;
>
> # Timeout value when the last known state was disconnected. 0 means infinite.
> degr-wfc-timeout 180;
> }
>
> syncer
> {
> # This is recommended only for low-bandwidth lines, to only send those
> # blocks which really have changed.
> #csums-alg md5;
>
> # Set to about half your net speed
> rate 60M;
>
> # It seems that this option moved to the 'net' section in drbd 8.4. (later release than Debian has currently)
> verify-alg md5;
> }
>
> net
> {
> # The manpage says this is recommended only in pre-production (because of its performance), to determine
> # if your LAN card has a TCP checksum offloading bug.
> #data-integrity-alg md5;
> }
>
> disk
> {
> # Detach causes the device to work over-the-network-only after the
> # underlying disk fails. Detach is not default for historical reasons, but is
> # recommended by the docs.
> # However, the Debian defaults in drbd.conf suggest the machine will reboot in that event...
> on-io-error detach;
>
> # LVM doesn't support barriers, so disabling it. It will revert to flush. Check wo: in /proc/drbd. If you don't disable it, you get IO errors.
> no-disk-barrier;
> }
>
> on host1
> {
> # universe is a VG
> disk /dev/universe/drbdvm-disk;
> address 10.0.0.1:7792;
> }
>
> on host2
> {
> # universe is a VG
> disk /dev/universe/drbdvm-disk;
> address 10.0.0.2:7792;
> }
> }
>
> In my test setup: the primary host's storage is 9650SE SATA-II RAID PCIe with battery. The secondary is software RAID1.
>
> Isn't DRBD+Xen widely used? With these problems, it's not going to work.
>
> Any help welcome.
>
> _______________________________________________
> drbd-user mailing list
> drbd-user at lists.linbit.com
> http://lists.linbit.com/mailman/listinfo/drbd-user
>
>
>
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