[Gluster-devel] Server-side AFR + Failover and mixed server/client-side AFR

[Derek Price]

Krishna Srinivas wrote:
>>  >  Is this an issue in server-side-only AFR? I have two servers which are also
>>  > clients of themselves, and they both list their local subvolume first and
>>  > remote subvolume second. Is this a problem? What are the possible
>>  > consequences of this?
>>
>>  It will be a problem. The "first" subvol is always the "lock" server.
>>  Consider a case where you are creating a file simultaneously
>>  on two clients, only one of them should succeed. If AFR's
>>  subvols order are not same, chances are that both client
>>  returns success for file creation with same name.
> 
> Hence you have "option read-subvlume" to speeden the
> read() calls so that it can be done from local subvol.

So, what happens if the "lock" server is the one that goes down?  Will 
that render the whole AFR cluster inoperable, at least for writes?

Why not arrange some sort of voting system for AFR locks, where no 
specific server, but rather half of the listed servers (maybe the first 
server listed gets an extra vote in the case of an even number of 
servers) have to agree to assign the lock (and increment the version # 
without receiving the data).  Then writes could also be done locally and 
synchronized at leisure.

Derek
-- 
Derek R. Price
Solutions Architect
Ximbiot, LLC <http://ximbiot.com>
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