[lustre-discuss] Draining and replacing OSTs with larger volumes

[Patrick Farrell]

Scott,

I’d like to strongly second all of Jongwoo’s advice, particularly that about adding new OSTs rather than replacing existing ones, if possible.  That procedure is so much simpler and involves a lot less messing around “under the hood”.  It takes you from a complex procedure with many steps to, essentially, copying a bunch of data around while your file system remains up, and adding and removing a few OSTs at either end.

It would also be non-destructive for your existing data.  One of the scary things about the original proposed process is that if something goes wrong partway through, the original data is already gone (or at least very hard to get).

Regards,
- Patrick
________________________________
From: lustre-discuss <lustre-discuss-bounces at lists.lustre.org> on behalf of Jongwoo Han <jongwoohan at gmail.com>
Sent: Thursday, February 28, 2019 5:36:54 AM
To: Scott Wood
Cc: lustre-discuss at lists.lustre.org
Subject: Re: [lustre-discuss] Draining and replacing OSTs with larger volumes



On Thu, Feb 28, 2019 at 11:09 AM Scott Wood <woodystrash at hotmail.com<mailto:woodystrash at hotmail.com>> wrote:
Hi folks,

Big upgrade process in the works and I had some questions.  Our current infrastructure has 5 HA pairs of OSSs and arrays with an HA pair of management and metadata servers who also share an array, all running lustre 2.10.3.  Pretty standard stuff.  Our upgrade plan is as follows:

1) Deploy a new HA pair of OSSs with arrays populated with OSTs that are twice the size of our originals.
2) Follow the process in section 14.9 of the lustre docs to drain all OSTs in one of existing the HA pairs' arrays
3) Repopulate the first old pair of deactivated and drained arrays with new larger drives
4) Upgrade the offline OSSs from 2.10.3 to 2.10.latest?
5) Return them to service
6) Repeat steps 2-4 for the other 4 old HA pairs of OSSs and OSTs

I'd expect this would be doable without downtime as we'd only be taking arrays offline that have no objects on them, and we've added new arrays and OSSs before with no issues.  I have a few questions before we begin the process:

1) My interpretation of the docs is that  we OK to install them with 2.10.6 (or 2.10.7, if it's out), as rolling upgrades withing X.Y are supported.  Is that correct?

In theory, rolling upgrade should work, but generally recommended upgrade procedure is to stop filesystem and unmount all MDS and OSS, upgrade package and bring them up. This will prevent human errors during repeated per-server upgrade.
When it is done correctly, It will take not more than 2 hours.

2) Until the whole process is complete, we'll have imbalanced OSTs.  I know that's not ideal, but is it all that big an issue

Rolling upgrade will cause imbalance, but after long run, the files will be assigned will be evenly distributed. No need to worry about it on one-shot upgrade scenario.

3) When draining the OSTs of files, section 14.9.3, point 2.a. states that the lfs find |lfs migrate can take multiple OSTs as args, but I thought it would be better to run one instance of that per OST and distribute them across multiple clients .  Is that reasonable (and faster)?

Parallel redistribute is generally faster than one-by-one. If the MDT can endure scanning load, run multiple migrate processes each for against one OST
4) When the drives are replaced with bigger ones, can the original OST configuration files be restored to them as described in Docs section 14.9.5, or due the the size mismatch, will that be bad?

Since this process will treat objects as files, the configurations should go as same.

5) What questions should I be asking that I haven't thought of?


I do not know the size of OSTs to deal with, but I think migrate(empty)-replace-migrate-replace is really painful process as it will take long time. If circumtances allow, I suggest add all new OST arrays to OSS with new OST nums, migrate OST objects, deactivate and remove old OSTs.

If that all goes well, and we did upgrade the OSSs to a newer 2.10.x, we'd follow it up with a migration of the MGT and MDT to one of the management servers, upgrade the other, fail them back, upgrade the second, and rebalance the MDT and MGT services back across the two.  We'd expect the usual pause in services as those migrate but other than that, fingers crossed, should all be good.  Are we missing anything?


If this plan is forced, rolling migrate and upgrade should be planned carefully. It will be better to set up correct procedure checklist by practicing on a virtual environment with identical versions.

Cheers
Scott
_______________________________________________
lustre-discuss mailing list
lustre-discuss at lists.lustre.org<mailto:lustre-discuss at lists.lustre.org>
http://lists.lustre.org/listinfo.cgi/lustre-discuss-lustre.org


--
Jongwoo Han
+82-505-227-6108
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.lustre.org/pipermail/lustre-discuss-lustre.org/attachments/20190228/17027090/attachment.html>