Re: [MooseFS-Users] converting to storage classes

[Agata Kruszona-Z. <ch...@mo...>]

W dniu 24.02.2021 o 00:15, William Kenworthy pisze:
> Hi,

Hi,

I've answered your questions below, but please note, that we moved with 
support and troubleshooting to github and if you want to look up answers 
to similar problems, you should go there. Also, I would like to 
encourage you to ask your own questions on github in the future.

https://github.com/moosefs/moosefs - main MooseFS repository.

https://github.com/moosefs/moosefs/discussions - new feature on Github, 
discussions, this is where people ask questions.

>      I have an approximately year old moosefs system with ~8GB data 
> (general data storage, email, lxc containers etc.) that was using goal 
> based allocation - I have added an ssd to and decided to use storage 
> classes to move one chunk of each of the lxc containers to the faster 
> SSD (seems to work well) while converting the the whole storage to 
> sclass based goal allocation.
> 
> To convert I did a mfssetsclass -r at the top of the mfs tree - after 
> removing older snapshots (I have read an email on how they handle the 
> conversion) I am left with ~580000 still with a goal of 3 that is 
> reported by the cli.
> 
> 1. how do I find which actual chunks are still at goal 3

You can't find that out directly, but you can make an educated guess and 
say they all belong to snapshotted files. So if/when you remove 
snapshots, all remaining chunks will move to appropriate storage classes 
automatically.

> 2. how can I map a chunk to a file

There is not a simple way to find out and there is no tool for that. 
This is because of the system architecture - files know, which chunks 
belogn to them, but chunks do not know, to which file(s) they belong. It 
can be done, but it requires dumping all your metadata CHNK and EDGE 
sections to text format and manually searching for the chunk in 
question, then from EDGEs you can rebuild the whole path of the file(s). 
If you are really interested in that, I can write you a short "how to".

> 3. I have used mfsmakesnapshot a bit indiscriminately and have likely 
> missed some snapshots - is there a way to identify chunks/files/dirs 
> belonging to a snapshot?

Yes, there is. You go to the root of your MooseFS instance and use this 
command:

mfsgeteattr *

If you see any entry, that has "snapshot" written after its name and ":" 
sign, it's a snanpshot.

To look deeper, you then use this command:

mfsgeteattr -r *

In the output, you look up all directories that have

not directory nodes with attribute         snapshot :          XXX
directories with attribute                 snapshot :          YYY

where either XXX or YYY is something else than 0. This directory 
contains a snapshot somewhere inside it, so you cd into it and repeat 
the procedure.

> The only way I can think of to remove unknown snapshotted data is to 
> copy the whole tree and delete the old one - which is a bit drastic!
> 
> Is there another mechanism that prevents some chunks from being 
> converted to a storage class? - or am I reading this wrong?

No, basically that's the only thing, that kind of "reverts to goal" - 
being part of a snapshot. All other chunks will be converted to a 
storage class (they still won't necessarily move to servers matching 
their storage class if something like lack of space or busy servers 
prevents this, but they will at least be trying to).

Regards,
Agata

--
Agata Kruszona-Zawadzka
MooseFS Team