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List:       linux-ha-dev
Subject:    Re: [Linux-ha-dev] heartbeat + nbd + raid1
From:       Marcelo Tosatti <marcelo () conectiva ! com ! br>
Date:       2000-04-16 12:06:16
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On Sat, 15 Apr 2000, Holger Kiehl wrote:

> nbd-client node2 1025 /dev/nd0       |
> losetup /dev/loop0 /home/nbd         |
> mkraid -c nbdtest /dev/md1           |
> mke2fs -b 4096 /dev/md1              |
> mount /dev/md1 /mnt                  |
> 
> Now each node will have the same filesystem. In the case that node2 should
> become active, the following steps would be necessary:
> 
>             node1                    |             node2 
> -------------------------------------+------------------------------------
> umount /mnt                          |
> stop nbd-client                      |
> losetup -d /dev/loop0                |
> nbd-server 1025 /home/nbd            |
>                                      | losetup /dev/loop0 /home/nbd
>                                      | nbd-client node1 1025 /dev/nd0
>                                      | raidstart /dev/md1
>                                      | mount /dev/md1 /mnt
> 
> When node2 would crash, the procedure would again be very similar:
> 
>             node1                    |             node2 
> -------------------------------------+------------------------------------
> losetup /dev/loop0 /home/nbd         |
> raidstart /dev/md1                   |
> fsck -p /dev/md1                     |
> mount /dev/md1 /mnt                  |
> 
> If node2 comes back online again the following steps are needed:
> 
>             node1                    |             node2 
> -------------------------------------+------------------------------------
>                                      | nbd-server 1025 /home/nbd
> nbd-client node2 1025 /dev/nd0       |
> raidhotadd /dev/md1 /dev/nd0         |
> 
> All this works very nicely when doing everything by hand and in the right
> order. Also the performance when writting to the nbd-raid-filesystem is
> very good when using a separate 100Mbit network.
> 
> However, it is difficult to get this in the right order with heartbeat.
> How can I for example detect the last case when node2 comes back after a
> crash? Another problem I see is, how can I stop the master node from
> starting a very old filesystem? For example the master node is down
> for a very long time and the secondary node is stopped or crashed. Now
> both are started again and the secondary node takes longer to come back,
> the primary node will start with a very old filesystem.
> 
> Has anyone done this nbd + raid1 + heartbeat? Or are there better ways of
> achieving this?
We are working on getting these problems fixed but not using raid1+nbd. 
Instead we are using drbd which is almost the same as RAID1+nbd but it has
advantages like a bitmap on memory which is used to resync dirty blocks.
You can get more info at http://www.complang.tuwien.ac.at/reisner/drbd/
(scripts to make it work with heartbeat are in the tarball).





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