[lustre-discuss] dne2: lfs setdirstripe

[Patrick Farrell]

Olaf,

I can explain the rationale for the restrictions, though I have not verified if the root only one applies to striped as well as remote directories.  (It's a simple test, though.  I'm just not where I can reach a test system.)

Note, to be clear: DNE 2 does not replace DNE 1.  Remote directories and striped directories are different things and can coexist.

For enable_remote_dir, it applies only to remote directories - not striped directories.  

As for the rationale: If enabled, it complicates things notably from an administrative perspective...  If you have multiple MDT changes in a path, it makes it harder to know what is where, and can cause files on, for example, MDT2 or MDT0, to become unreachable if MDT1 is lost.  Also, if you think carefully, it doesn't really enable any use cases that can't be done otherwise - at least, none that we could find that seemed practical.

As far as the root only thing:
Imagine you are trying to split the load between your MDTs by assigning particular users to particular MDTs.  If your users can create their own remote directories, they can escape this restriction.  Also, you can open up permission by setting it to -1.

I learned this by a mix of reading design docs, experimenting, and being at least tangentially involved via the PAC.
I'd suggest design docs as a good place to look for more.

- Patrick Farrell
________________________________________
From: lustre-discuss [lustre-discuss-bounces at lists.lustre.org] on behalf of Faaland, Olaf P. [faaland1 at llnl.gov]
Sent: Wednesday, September 02, 2015 5:21 PM
To: lustre-discuss at lists.lustre.org
Subject: Re: [lustre-discuss] dne2: lfs setdirstripe

The lustre we are testing with is built from commit

ea383222e031cdceffbdf2e3afab3b6d1fd53c8e

which is after tag 2.7.57 but before 2.7.59; so recent but not entirely current.

Olaf P. Faaland
Livermore Computing
phone : 925-422-2263
________________________________
From: lustre-discuss [lustre-discuss-bounces at lists.lustre.org] on behalf of Faaland, Olaf P. [faaland1 at llnl.gov]
Sent: Wednesday, September 02, 2015 3:17 PM
To: lustre-discuss at lists.lustre.org
Subject: [lustre-discuss] dne2: lfs setdirstripe

Hi,

We have begun work on testing DNE with ZFS backend.  So far we've only done the installation of the filesystem and begun educating ourselves.

I see in man lfs, that "lfs setdirstripe" has some restrictions by default
 - only executable by root unless "mdt.*.enable_remote_dir_gid" is set
 - only directories on MDT0000 can contain directories that are not on the same MDT unless "mdt.*.enable_remote_dir"

1. Are those restrictions still current, or do they refer to DNE phase 1 restrictions that no longer apply?

2. If the first, allowing only root to invoke "lfs setdirstripe" is current, what is the rationale?

3. Is there documentation, or a mailing list thread, that we should read prior to posting questions?

Thanks,

Olaf P. Faaland
Livermore Computing
phone : 925-422-2263