Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On 19 Sep 2016 5:45 pm, "Marco Marino" <marino.mrc at gmail.com> wrote:
>
> Hi, I'm trying to build an active/passive cluster with drbd and pacemaker
for a san. I'm using 2 nodes with one raid controller (megaraid) on each
one. Each node has an ssd disk that works as cache for read (and write?)
realizing the CacheCade proprietary tecnology.
>
Did you configure the CacheCade? If the write cache was enabled in
write-back mode then suddenly removing the device from under the controller
would have caused serious problems I guess since the controller expects to
write to the ssd cache firts and then flush to the hdd's. Maybe this
explains the read only mode?
> Basically, the structure of the san is:
>
> Physycal disks -> RAID -> Device /dev/sdb in the OS -> Drbd resource
(that use /dev/sdb as backend) (using pacemaker with a master/slave
resource) -> VG (managed with pacemaker) -> Iscsi target (with pacemaker)
-> Iscsi LUNS (one for each logical volume in the VG, managed with
pacemaker)
>
> Few days ago, the ssd disk was wrongly removed from the primary node of
the cluster and this caused a lot of problems: drbd resource and all
logical volumes went in readonly mode with a lot of I/O errors but the
cluster did not switched to the other node. All filesystem on initiators
went to readonly mode. There are 2 problems involved here (I think): 1) Why
removing the ssd disk cause a readonly mode with I/O errors? This means
that the ssd is a single point of failure for a single node san with
megaraid controllers and CacheCade tecnology..... and 2) Why drbd not
worked as espected?
What was the state in /proc/drbd ?
> For point 1) I'm checking with the vendor and I doubt that I can do
something
> For point 2) I have errors in the drbd configuration. My idea is that
when an I/O error happens on the primary node, the cluster should switch to
the secondary node and shut down the damaged node.
> Here -> http://pastebin.com/79dDK66m it is possible to see the actual
drbd configuration, but I need to change a lot of things and I want to
share my ideas here:
>
> 1) The "handlers" section should be moved in the "common" section of
global_common.conf and not in the resource file.
>
> 2)I'm thinking to modify the "handlers" section as follow:
>
> handlers { pri-on-incon-degr "/usr/lib/drbd/notify-pri-on-incon-degr.sh;
/usr/lib/drbd/notify-emergency-reboot.sh; echo b > /proc/sysrq-trigger ;
reboot -f"; pri-lost-after-sb "/usr/lib/drbd/notify-pri-lost-after-sb.sh;
/usr/lib/drbd/notify-emergency-reboot.sh; echo b > /proc/sysrq-trigger ;
reboot -f"; local-io-error "/usr/lib/drbd/notify-io-error.sh;
/usr/lib/drbd/notify-emergency-shutdown.sh; echo o > /proc/sysrq-trigger ;
halt -f"; # Hook into Pacemaker's fencing. fence-peer
"/usr/lib/drbd/crm-fence-peer.sh"; }
>
>
> In this way, when an I/O error happens, the node will be powered off and
pacemaker will switch resources to the other node (or at least doesn't
create problematic behaviors...)
>
> 3) I'm thinking to move the "fencing" directive from the resource to the
global_common.conf file. Furthermore, I want to change it to
>
> fencing resource-and-stonith;
>
>
> 4) Finally, in the global "net" section I need to add:
>
> after-sb-0pri discard-zero-changes; after-sb-1pri discard-secondary;
after-sb-2pri disconnect;
>
> At the end of the work configuration will be ->
http://pastebin.com/r3N1gzwx
>
> Please, give me suggestion about mistakes and possible changes.
>
> Thank you
>
>
>
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>
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