Re: 3.7.13, index healing broken?

[Dmitry Melekhov <dm@xxxxxxxxxx>]

13.07.2016 10:10, Pranith Kumar Karampuri пишет:

On Wed, Jul 13, 2016 at 11:27 AM, Dmitry Melekhov <dm@xxxxxxxxxx> wrote:

13.07.2016 09:50, Pranith Kumar Karampuri пишет:

On Wed, Jul 13, 2016 at 11:11 AM, Dmitry Melekhov <dm@xxxxxxxxxx> wrote:

13.07.2016 09:36, Pranith Kumar Karampuri пишет:

On Wed, Jul 13, 2016 at 10:58 AM, Dmitry Melekhov <dm@xxxxxxxxxx> wrote:

13.07.2016 09:26, Pranith Kumar Karampuri пишет:

On Wed, Jul 13, 2016 at 10:50 AM, Dmitry Melekhov <dm@xxxxxxxxxx> wrote:

13.07.2016 09:16, Pranith Kumar Karampuri пишет:

On Wed, Jul 13, 2016 at 10:38 AM, Dmitry Melekhov <dm@xxxxxxxxxx> wrote:

13.07.2016 09:04, Pranith Kumar Karampuri пишет:

On Wed, Jul 13, 2016 at 10:29 AM, Dmitry Melekhov <dm@xxxxxxxxxx> wrote:

13.07.2016 08:56, Pranith Kumar Karampuri пишет:

On Wed, Jul 13, 2016 at 10:23 AM, Dmitry Melekhov <dm@xxxxxxxxxx> wrote:

13.07.2016 08:46, Pranith Kumar Karampuri пишет:

On Wed, Jul 13, 2016 at 10:10 AM, Dmitry Melekhov <dm@xxxxxxxxxx> wrote:

13.07.2016 08:36, Pranith Kumar Karampuri пишет:

On Wed, Jul 13, 2016 at 9:35 AM, Dmitry Melekhov <dm@xxxxxxxxxx> wrote:

13.07.2016 01:52, Anuradha Talur пишет:

----- Original Message -----

From: "Dmitry Melekhov" <dm@xxxxxxxxxx>
To: "Pranith Kumar Karampuri" <pkarampu@xxxxxxxxxx>
Cc: "gluster-users" <gluster-users@xxxxxxxxxxx>
Sent: Tuesday, July 12, 2016 9:27:17 PM
Subject: Re: 3.7.13, index healing broken?



12.07.2016 17:39, Pranith Kumar Karampuri пишет:



Wow, what are the steps to recreate the problem?

just set file length to zero, always reproducible.

If you are setting the file length to 0 on one of the bricks (looks like
that is the case), it is not a bug.

Index heal relies on failures seen from the mount point(s)
to identify the files that need heal. It won't be able to recognize any file
modification done directly on bricks. Same goes for heal info command which
is the reason heal info also shows 0 entries.

Well, this makes self-heal useless then- if any file is accidently corrupted or deleted (yes! if file is deleted directly from brick this is no recognized by idex heal too), then it will not be self-healed, because self-heal uses index heal.

It is better to look into bit-rot feature if you want to guard against these kinds of problems.

Bit rot detects bit problems, not missing files or their wrong length, i.e. this is overhead for such simple task.

It detects wrong length. Because checksum won't match anymore.

Yes, sure. I guess that it will detect missed files too. But it needs far more resources, then just comparing directories in bricks?

What use-case you are trying out is leading to changing things directly on the brick?

I'm trying to test gluster failure tolerance and right now I'm not happy with it...

Which cases of fault tolerance are you not happy with? Making changes directly on the brick or anything else as well?

I'll repeat:
As I already said- if I for some reason ( real case  can be only by accident ) will delete file this will not be detected by self-heal daemon, and, thus, will lead to lower replication level, i.e. lower failure tolerance.

To prevent such accidents you need to set selinux policies so that files under the brick are not modified by accident by any user. At least that is the solution I remember when this was discussed 3-4 years back.

So only supported platfrom is linux? Or, may be, it is better to improve self-healing to detect missing or wrong length files, I guess this is very low cost in terms of host resources operation.
Just a suggestion, may be we need to look to alternatives in near future....

This is a corner case, from design perspective it is generally not a good idea to optimize for the corner case. It is better to protect ourselves from the corner case (SElinux etc) or you can also use snapshots to protect against these kind of mishaps.

Sorry, I'm not agree.
As you  know if on access missed or wrong lenghted file from fuse client it is restored (healed), i.e. gluster recognizes file is wrong and heal it , so I do not see any reason to provide this such function as self-healing.
Thank you!

Ah! Now how do you suggest we keep track of which of 10s of millions of files the user accidentally deleted from the brick without gluster's knowledge? Once it comes to gluster's knowledge we can do something. But how does gluster become aware of something it is not keeping track of? At the time you access it gluster knows something went wrong so it restores it. If you change something on the bricks even by accident all the data gluster keeps (similar to journal) is a waste. Even the disk filesystems will ask you to do fsck if something unexpected happens so full self-heal is similar operation.

You are absolutely right- question is why gluster does not become aware about such problem is case of self-healing?

Because the operations that are performed directly on brick do not go through gluster stack.

 

OK, I'll repeat- 
As you  know if on access missed or wrong lenghted file from fuse client it is restored (healed), i.e. gluster recognizes file is wrong and heal it , so I do not see any reason to provide this such function as self-healing.

For which you need accessing the file.

That's right.

For which you need full crawl. You can't detect the modification which doesn't go through the stack so this is the only possibility.

OK, then, if self-heal is really useless and no possible way to get it will be provided, I guess we'll use external script to check bricks directories consistency,
don't think ls and diff will get much resources.

How is this different from full self-heal?

Self-heal does not detect deleted or wrong-length files .
Why it can't ? I don't know, you just said it is impossible in gluster because it can only track changes only made through gluster, i.e. bricks can have different files sets and it is not recognized (true) because , as I understand, gluster's  self-heal thinks that brick underlying filesystem can't be corrupted by server admin  (not true, I can say this as almost 25 years experienced engineer, i.e. I did this several times ;-) ).

 

Thank you!

p.s.
still can't understand why it can't be implemented in gluster... :-(

--

Pranith

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Pranith

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Pranith

--

Pranith

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