Re: [Gluster-devel] Fwd: Behaviour of simple distributed volumes on failed bricks?

[Raghavendra G <raghavendra.hg@xxxxxxxxx>]

On Thu, Jan 12, 2017 at 4:44 PM, Raghavendra G <raghavendra.hg@xxxxxxxxx> wrote:

On Thu, Jan 12, 2017 at 4:35 PM, Raghavendra G <raghavendra.hg@xxxxxxxxx> wrote:

On Thu, Jan 12, 2017 at 9:20 AM, B.K.Raghuram <bkrram@xxxxxxxxx> wrote:

cc'ing devel as well for some developer insight..

---------- Forwarded message ----------
To: gluster-users <gluster-users@xxxxxxxxxxx>

I had a question on the expected behaviour of simple distributed volumes when a brick fails for the following scenarios (as in, will the scenario succeed for fail) :

- New file creation if that file name hashes to the failed brick

Fails

 

- New file creation if that file name hashes to one of the remaining functional brick

Succeeds

- New directory creation if that file name hashes to the failed brick

Fails

 

- New directory creation if that file name hashes to one of the remaining functional brick

Succeeds. Layout is spread only to the functional bricks. Non-functional bricks are not part of layout of the directory. In other words files of the directory won't be stored in non-functional bricks
 

- File modifications/deletions if that file name hashes to the failed brick

Fails

Fails mostly. However, let's say if the inode of file has been looked up when hashed-brick was up, then operations succeed even if hashed-brick goes down later.

Sorry, I forgot to mention that this can happen only if actual file (data-file) is stored on non-hashed brick and hashed-brick contains a linkto file. If data-file is present on hashed brick and it goes down, access fails always.

Following sequence of ops succeed:

1. hashed-brick up

2. Lookup (file) => success

3. open (file) => success (fd)

4. hashed-brick goes down

5. write/read (fd) => success

 

Note that if the inode is cached in vfs/kernel after 2, even path based operations like stat, open, chmod etc can succeed if hashed-brick goes down immediately after successful lookup. The point is only fresh lookups fail if hashed brick/subvol is down.

 

- File modifications/deletions if that file name hashes to one of the remaining functional brick

Succeeds
 

- Directory renames/deletions if that file name hashes to the failed brick

Fails
 

- Directory renames/deletions if that file name hashes to one of the remaining functional brick

Fails
 

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Raghavendra G

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Raghavendra G

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Raghavendra G

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