[Lustre-devel] SOM Recovery of open files

Vitaly Fertman Vitaly.Fertman at Sun.COM
Sun Feb 1 09:24:41 PST 2009

On Feb 1, 2009, at 5:45 PM, Vitaly Fertman wrote:

> thus the only problem here is a stale fh on a client which may let  
> the client
> to write to the file after the SOM cache will be re-obtained on MDS,  
> which
> consists of 2 parts:
> - an ability of a client to write to an opened file without a  
> connection to MDS;
> - an absence of file re-opening on re-connection.

I forgot to mention about truncate (locked & lockless) and lockless IO.

MDS must be aware about opened IOEpoch for truncate as well, otherwise
obd_punches must be blocked. The situation is pretty rare as we do not
cache punches on clients and they go away right md_setattr completes,
but I think what if at the time of the client eviction from MDS, the  
between this client and an OST is unstable so that punches will hang  
in the
re-send list for a while, enough for another client to modify the file  
MDS gets a new SOM cache, and later punch will modify the file.

The same for lockless IO.

The locked truncate is involved as it could hang in the re-send list  
the lock enqueue, so that enqueue+punch will happen after MDS re- 
SOM cache.

- block truncate and lockless IO;
- "re-open" truncate on re-connection as well as regularly opened files.

This must happen even if SOM is disabled but the client already  
supports it
(clients are upgraded first). Otherwise, the interoperability will be  


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