Re: How to calculate used rate of a OST ?

swin wang wrote:
> We have tested the 1.5.97,  and set qos_priofree,  but  it  didn't work,
> I think qos_priofree just make different penalty to OST, it can not avoid
> alloc object on the full OST.
> Are you sure qos_priofree can do it?
You are correct; it just changes the penalty.  QOS does not ever 
guarantee that any particular OST will or won't be used - it only 
changes the likelihood. 

You can prevent the MDT from assigning new stripes to a particular OST 
by deactivating the corresponding OSC on the MDT using "lctl 
deactivate", but this has to be done every time the MDT is restarted.  
You could also use

mount -o exclude=testfs-OST0000 -t lustre /dev/mdt /mnt/mdt

at MDT mount time for the same result.

You could also change the line in filter_precreate()
if (rc == 0 && osfs->os_bavail < (osfs->os_blocks >> 10))
blocks >> 10 = blocks / 1024 = 0.1%,
you could just change it to os_blocks / 10 for an automatic 10% free 
space limit.

> 2007/4/18, Andreas Dilger <adilger-KYPl3Ael/zSakBO8gow8eQ@xxxxxxxxxxxxxxxx 
> <mailto:adilger-KYPl3Ael/zSakBO8gow8eQ@xxxxxxxxxxxxxxxx>>:
>
>     On Apr 18, 2007  16:19 +0800, swin wang wrote:
>     >    We hope that if an OST's used rate up to 90% or 95%, it can
>     be marked
>     > FULL, and avoid to use this OST. we plan to add a state FULL in
>     structure
>     > lov_tgt_desc, when the
>     > OST  used  rate up to  90% or 95%, set its state to FULL, and
>     when create
>     > new object,
>     > don't use these FULL OST.
>     >    We want to know how to calculate used rate of a  OST,  is it
>     like this:
>     >        used rate =
>     lov->lov_tgts[i]->ltd_exp->exp_obd->obd_osfs.os_bavail /
>     > ov->lov_tgts[i]->ltd_exp->exp_obd->obd_osfs.os_blocks  ??
>
>     This is already done on the OSTs in filter_precreate(), though the
>     limit is
>     only 0.1%.  I'd be happy to accept a patch which made this limit a
>     tunable
>     in /proc that can be set by the sysadmin.
>
>     There is also in 1.6 (and betas) some free space management that
>     is tunable
>     on the MDS /proc/fs/lustre/lov/*/qos_priofree which is a
>     percentage of
>     weight which you want to give to "free" OSTs.  In your case you
>     want this
>     to be relatively high (90% is the default in later betas).  If
>     this is not
>     sufficient to have the MDS allocate very preferentially on free
>     OSTs, please
>     provide more details on your configuration.
>
>     Cheers, Andreas
>     --
>     Andreas Dilger
>     Principal Software Engineer
>     Cluster File Systems, Inc.
>
>
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