[sheepdog-users] Node Recovery

[Takashi Menjo]

Hi Pee Tee,

> UPDATE:
> 
> It is not re-building.  Recheck of I/O activity via IOTOP shows ONLY reads
> of disk holding cluster (same approximate amount of reads on both nodes)

It looks like both nodes read VDIs' chunks to calculate their message
digest.

When a node without data loss re-joins a cluster, it checks whether
each chunk that it has had was updated by other node(s) or not.
If not, that node repairs that chunk by itself.

In this checking process, **each node reads chunks from disk**
to calculate and exchange their message digest.

I think the disk read you observed was due to **this**.

Regards,
-- 
Takashi Menjo <menjo.takashi at lab.ntt.co.jp>

> -----Original Message-----
> From: sheepdog-users [mailto:sheepdog-users-bounces at lists.wpkg.org] On
> Behalf Of Pee Tee
> Sent: Tuesday, January 31, 2017 9:26 PM
> To: sheepdog-users at lists.wpkg.org
> Subject: [sheepdog-users] Node Recovery
> 
> A slight confusion on my part in terms of node recovery -
> 
> Using Sheepdog 0.8.3 on Ubuntu 16.04 with Corosync and a simple setup.
> 
> I have 2 KVM servers set up and 1 cluster.
> 
> I have 2 VDI's in the cluster both of 20gb.
> 
> Neither VDI is active in the 2 KVM servers (i.e.all virtual machines
stopped).
> 
> Now:-
> 
> If i reboot (normal shutdown) a server (say node 0) on restart it says
"node
> 0 in recovery" - it than seems to be rebuilding the VDI's on node zero
(some
> 40gb of I/O).  Each time I reboot, the same occurs.
> 
> This somewhat confuses me.  Both VDI disks are identical on each node, no
> updates/writes have occurred - surely Sheepdog should know nothing has
> change?
> 
> What if I expand  this out to a Terabyte of VDI's - taking a node down for
> maintenance will incur massive delay on restart.
> 
> Am I doing something wrong?
> 
> UPDATE:
> 
> It is not re-building.  Recheck of I/O activity via IOTOP shows ONLY reads
> of disk holding cluster (same approximate amount of reads on both nodes)
> --
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