[lustre-discuss] set OSTs read only ?

[Alexander I Kulyavtsev]

You may find advise from Andreas on this list (also attached below). I did not try setting fail_loc myself.

In 2.9 there is setting  osp.*.max_create_count=0 described at LUDOC-305.

We used to set OST degraded as described in lustre manual.
It works most of the time but at some point I saw lustre errors in logs for some ops. Sorry, I do not recall details.

I still not sure either of these approaches will work for you: setting OST degraded or fail_loc will makes some osts selected instead of others.
You may want to verify if these settings will trigger clean error on user side (instead of blocking) when all OSTs are degraded.

The other and also simpler approach would be to enable lustre quota and set quota below used space for all users (or groups).

Alex.

From: "Dilger, Andreas" <andreas.dilger at intel.com<mailto:andreas.dilger at intel.com>>
Subject: Re: [lustre-discuss] lustre 2.5.3 ost not draining
Date: July 28, 2015 at 11:51:38 PM CDT
Cc: "lustre-discuss at lists.lustre.org<mailto:lustre-discuss at lists.lustre.org>" <lustre-discuss at lists.lustre.org<mailto:lustre-discuss at lists.lustre.org>>

Setting it degraded means the MDS will avoid allocations on that OST
unless there aren't enough OSTs to meet the request (e.g. stripe_count =
-1), so it should work.

That is actually a very interesting workaround for this problem, and it
will work for older versions of Lustre as well.  It doesn't disable the
OST completely, which is fine if you are doing space balancing (and may
even be desirable to allow apps that need more bandwidth for a widely
striped file), but it isn't good if you are trying to empty the OST
completely to remove it.

It looks like another approach would be to mark the OST as having no free
space using OBD_FAIL_OST_ENOINO (0x229) fault injection on that OST:

  lctl set_param fail_loc=0x229 fail_val=<ost_index>

This would cause the OST to return 0 free inodes from OST_STATFS for the
specified OST index, and the MDT would skip this OST completely.  To
disable all of the OSTs on an OSS use <ost_index> = -1.  It isn't possible
to selectively disable a subset of OSTs using this method.  The
OBD_FAIL_OST_ENOINO fail_loc has been available since Lustre 2.2, which
covers all of the 2.4+ versions that are affected by this issue.

If this mechanism works for you (it should, as this fail_loc is used
during regular testing) I'd be obliged if someone could file an LUDOC bug
so the manual can be updated.

Cheers, Andreas


On Jul 12, 2017, at 4:20 PM, Riccardo Veraldi <Riccardo.Veraldi at cnaf.infn.it<mailto:Riccardo.Veraldi at cnaf.infn.it>> wrote:

Hello,

on one of my lustre FS I need to find a solution so that users can still
access data on the FS but cannot write new files on it.
I have hundreds of clients accessing the FS so remounting it ro is not
really easily feasible.
Is there an option on the OSS side to allow OSTs to be accessed just to
read data and not to store new data ?
tunefs.lustre could do that ?
thank you

Rick

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