[Lustre-discuss] Confusion regarding deactivating OSTs

[Andreas Dilger]

It is possible for the clients to mount the whole Filesystem read-only, which sets a flag on the MDS and OST for that client to have it return -EROFS for any Filesystem modifying operations.

However, it isn't possible to mount the OST itself read-only today. At one time there were patches in bugzilla that started to investigate this but they were never finished and landed.

I suspect it wouldn't be too much worknfor someone to try mounting the OST with the "-o ro" mount option and then fixing the few places at mount time that are depending on being able to write to the filesystem. At the same time, I suspect that this isn't what you want to be doing when your system is already down, so it will have to be at a later time perhaps. 

Cheers, Andreas

On 2010-07-09, at 12:00, Adeyemi Adesanya <yemi at slac.stanford.edu> wrote:

> 
> 
> Hi.
> 
> We are attempting to recover from a RAID controller issue in a storage  
> array that holds a couple of OSTs. We would like to tread carefully  
> and eventually remount the OSTs read-only so that clients can read  
> files striped to these OSTs but not write data. According to the 1.8  
> manual, running 'lctl deactivate' on just the MDS will prevent new  
> objects from being allocated to the OST but will allow reads AND  
> writes to existing objects. Is there any way of preventing all kinds  
> of write activity to the OST (not just new object creation)?
> 
> -------
> Yemi
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