Re: attack upon XFS, misinformation abounds, linux-raid list

From: Eric Sandeen <sandeen@sandeen.net>
To: Stefan Ring <stefanrin@gmail.com>
Cc: stan@hardwarefreak.com, "xfs@oss.sgi.com" <xfs@oss.sgi.com>
Subject: Re: attack upon XFS, misinformation abounds, linux-raid list
Date: Mon, 10 Jun 2013 08:44:04 -0500	[thread overview]
Message-ID: <51B5D824.3060704@sandeen.net> (raw)
In-Reply-To: <CAAxjCEznq0RDnnYR_mQ=gmSeson4acyiLVcVdOh2vmQo1cVAzA@mail.gmail.com>

On 6/10/13 4:43 AM, Stefan Ring wrote:
> On Sun, Jun 9, 2013 at 12:46 PM, Stan Hoeppner <stan@hardwarefreak.com> wrote:
>> In a recent linux-raid list thread here:
>> http://marc.info/?l=linux-raid&m=137072140106867&w=2
>>
>> seriously flawed arguments against the reliability of XFS, and even the
>> performance of XFS, are made.  The OP even quotes Dave's LCA
>> presentation as a performance reason to avoid XFS.  The party really
>> gets started at paragraph 7.
>>
>> I made a brief effort to debunk his claims and explained that he can't
>> have O_PONIES, that he should use fsync or O_DIRECT, etc for data
>> safety.  To non experts/advanced filesystem users, his long winded
>> argument may be persuasive.  Obviously none of you experts has time to
>> debunk every such post, but this one may be worth a read at least,
>> especially given the weight Google gives to vger lists.
> 
> The really unfortunate thing about this is that the bug[1] which would
> prevent transaction flushing from happening got imported and shipped
> for a rather long time in RHEL. It's one thing to get a file zeroed
> that's a few seconds old, but having the same happen to files which
> haven't been touched in hours, even before issuing manual sync, is
> certainly not very reassuring.

Bugs and regressions are always unfortunate, and this one was no exception.
It was pretty obscure, but we (mostly Dave) worked with our customers
to identify & resolve it within days of the bug report.

As far as I know, the bug existed only for a crash, not a reboot.

> As a very satisfied user of XFS on CentOS 6, I have been nervous
> enough about that to go through the trouble of rebooting our main
> server for a kernel upgrade a few weeks ago. Thanks to RedHat's
> deceptive tactics regarding kernel patches, I have also not been able

deceptive - adj. - Giving an appearance or impression different from the true one; misleading.

which sounds pretty damning.  Perhaps more accurate is:

obfuscated - adj. - Rendered obscure, unclear, or unintelligible ;)

> to pin-point the exact range of kernel versions affected by this in a
> reasonable amount of time and hence have not found out (thankfully not
> the hard way) if it was even necessary.

It was introduced in 6.2 and resolved in 6.4, as well as 6.2
and 6.3 z-stream kernels.  Those are the sorts of things Red Hat support
can help customers identify more quickly & clearly.

-Eric

> [1] https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/6.4_Technical_Notes/kernel.html
> "BZ#855139"
> 
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