Questions about XFS

Questions about XFS

[clflush]

Hi,

I have a few simple questions regarding the XFS file system. I built a new 
small server here (commodity hardware, x86-64) and I've installed 32-bit 
openSUSE 10.2 on it. After the system was installed, configured and up and 
running, it hung while I was browsing with Firefox. The only thing I could do 
was to press the reset button on the computer. After the reboot, when I 
opened Firefox again, I noticed that all my bookmarks were gone. Those 
bookmarks were imported from my desktop machine a few days after I configured 
the new server.

All file systems on this new server are XFS because I heard good things about 
it and it generally performs better in database operations compared to other 
file systems available for Linux. However, I was pretty surprised that when I 
had to reset the machine because it hung for some reason, all the bookmarks 
in Firefox were gone, so now I have my doubts about the reliability and data 
integrity of XFS. My older server, which also runs openSUSE 10.2 (32-bit) but 
uses Ext3 as file system never had such issues and I had to reset it many 
times because it was hanging for some reason.

Am I right to assume that XFS compared to Ext3 does not do a very good job 
regarding data integrity? I know a little bit about file systems and I know 
that most file systems depend on the application to do the right job 
regarding the way it opens/locks/saves files, but in reality not all 
applications are written in a safe way to guarantee this.

Basically, my two question that I have are:

- Why did I lost bookmarks on a machine running XFS while on another one which 
runs the same OS version but uses Ext3 as file system, it never happened, no 
matter how many times I had to reset it.

- Are there any efforts currently made to increase the data integrity of XFS?

Regards

Re: Questions about XFS

[Klaus Strebel]

clflush schrieb:
> Hi,
> 
> I have a few simple questions regarding the XFS file system. I built a new 
> small server here (commodity hardware, x86-64) and I've installed 32-bit 
> openSUSE 10.2 on it. After the system was installed, configured and up and 
> running, it hung while I was browsing with Firefox. The only thing I could do 
> was to press the reset button on the computer. After the reboot, when I 
> opened Firefox again, I noticed that all my bookmarks were gone. Those 
> bookmarks were imported from my desktop machine a few days after I configured 
> the new server.
> 
> All file systems on this new server are XFS because I heard good things about 
> it and it generally performs better in database operations compared to other 
> file systems available for Linux. However, I was pretty surprised that when I 
> had to reset the machine because it hung for some reason, all the bookmarks 
> in Firefox were gone, so now I have my doubts about the reliability and data 
> integrity of XFS. My older server, which also runs openSUSE 10.2 (32-bit) but 
> uses Ext3 as file system never had such issues and I had to reset it many 
> times because it was hanging for some reason.
> 
> Am I right to assume that XFS compared to Ext3 does not do a very good job 
> regarding data integrity? I know a little bit about file systems and I know 
> that most file systems depend on the application to do the right job 
> regarding the way it opens/locks/saves files, but in reality not all 
> applications are written in a safe way to guarantee this.
> 
> Basically, my two question that I have are:
> 
> - Why did I lost bookmarks on a machine running XFS while on another one which 
> runs the same OS version but uses Ext3 as file system, it never happened, no 
> matter how many times I had to reset it.
> 
> - Are there any efforts currently made to increase the data integrity of XFS?
> 
> Regards
> 
> 
Hi,

short and rude answer: 'Search the archives and FAQs'.

Simply short answer: no and no.

Longer answer: XFS only cares about meta-data integrity, if unwritten 
extends exist in memory, you'll get these empty on the disk if you reset 
your box. You should consider using the 'Magic SysRq' hotkeys to 
emergency sync your disk in cases like these before you reset your box.

Ciao
Klaus

-- 
Mit freundlichen Grüssen / best regards

Klaus Strebel, Dipl.-Inform. (FH), mailto:klaus.strebel@gmx.net

/"\
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  X        AGAINST HTML MAIL
/ \

Re: Questions about XFS

[Stein M. Hugubakken]

clflush wrote:
> Basically, my two question that I have are:
> 
> - Why did I lost bookmarks on a machine running XFS while on another one which 
> runs the same OS version but uses Ext3 as file system, it never happened, no 
> matter how many times I had to reset it.
> 
> - Are there any efforts currently made to increase the data integrity of XFS?
> 

Take a look at the FAQ:
http://oss.sgi.com/projects/xfs/faq.html#wcache

Regarding the lost bookmarks, you might find an old backup in 
~/.mozilla/firefox/<userprofile>/bookmarkbackups.

Regards
Stein

Re: Questions about XFS

[Eric Sandeen]

clflush wrote:
> Hi,
> 
> I have a few simple questions regarding the XFS file system. I built a new 
> small server here (commodity hardware, x86-64) and I've installed 32-bit 
> openSUSE 10.2 on it. After the system was installed, configured and up and 
> running, it hung while I was browsing with Firefox. The only thing I could do 
> was to press the reset button on the computer. After the reboot, when I 
> opened Firefox again, I noticed that all my bookmarks were gone. Those 
> bookmarks were imported from my desktop machine a few days after I configured 
> the new server.
> 
> All file systems on this new server are XFS because I heard good things about 
> it and it generally performs better in database operations compared to other 
> file systems available for Linux. However, I was pretty surprised that when I 
> had to reset the machine because it hung for some reason, all the bookmarks 
> in Firefox were gone, so now I have my doubts about the reliability and data 
> integrity of XFS. My older server, which also runs openSUSE 10.2 (32-bit) but 
> uses Ext3 as file system never had such issues and I had to reset it many 
> times because it was hanging for some reason.

sounds like you have several reliability problems ;-)

> Am I right to assume that XFS compared to Ext3 does not do a very good job 
> regarding data integrity? I know a little bit about file systems and I know 
> that most file systems depend on the application to do the right job 
> regarding the way it opens/locks/saves files, but in reality not all 
> applications are written in a safe way to guarantee this.
> 
> Basically, my two question that I have are:
> 
> - Why did I lost bookmarks on a machine running XFS while on another one which 
> runs the same OS version but uses Ext3 as file system, it never happened, no 
> matter how many times I had to reset it.

see also http://oss.sgi.com/projects/xfs/faq.html#nulls

> - Are there any efforts currently made to increase the data integrity of XFS?

this is essentially a loss of buffered data in the VM, outside the realm 
of what xfs can realistically protect.  With ext3, you probably were 
losing your "latest" bookmarks as well, but were luckily(?) getting back 
whatever used to be on-disk.

On the other hand, there were some changes made to xfs to explicitly 
sync files on close, if they have been truncated, which should help this 
sort of problem.  Depending on what's in OpenSuSE 10.2, that change may 
or may not be in your code...

-Eric

Re: Questions about XFS

[Stewart Smith]

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On Tue, 2007-03-13 at 14:40 +0100, clflush wrote:
> I have a few simple questions regarding the XFS file system. I built a new 
> small server here (commodity hardware, x86-64) and I've installed 32-bit 
> openSUSE 10.2 on it. After the system was installed, configured and up and 
> running, it hung while I was browsing with Firefox. The only thing I could do 
> was to press the reset button on the computer. After the reboot, when I 
> opened Firefox again, I noticed that all my bookmarks were gone. Those 
> bookmarks were imported from my desktop machine a few days after I configured 
> the new server.

This is a firefox bug - I've seen it before (on my mother's machine).

It's due to firefox not doing the correct thing with IO on the bookmarks
file.

As mentioned in another mail you can restore from a backup that firefox
makes.

In a future release, firefox is going to be using sqlite for storing
thes ethings, which will mean that these problems go away (pretty sure
sqllite does all the right things)
-- 
Stewart Smith (stewart@flamingspork.com)
http://www.flamingspork.com/


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Re: Questions about XFS

[Taisuke Yamada]

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Hash: SHA1

- From end-user's POV, this infamous XFS behavior is somewhat
taken as XFS's inferiority compared to other filesystems.
Even with "bad" applications (ex. firefox), this rarely happens
on others, so regardless of what's on the FAQ, people logically
concludes that the fault belongs to XFS anyway.

So, what is the correct way to do IO?
Is what firefox (and other bad apps) doing is so obvious(ly buggy),
that it'll be acknowledged as a bug once reported? Or is it simply
a mismatch between application expectation and XFS behavior,
requiring a non-(obvious|generic) fix?

Although I'm not a filesystem developer, I'm pretty impressed with
XFS and willing to file a report/patch to those "buggy" apps if the
issue is explainable to other app developers.

>> was to press the reset button on the computer. After the reboot, when I 
>> opened Firefox again, I noticed that all my bookmarks were gone. Those 
>> bookmarks were imported from my desktop machine a few days after I configured 
>> the new server.
> 
> This is a firefox bug - I've seen it before (on my mother's machine).
> 
> It's due to firefox not doing the correct thing with IO on the bookmarks
> file.

- --
Taisuke Yamada <tyamadajp@spam.rakugaki.org>, http://rakugaki.org/
2268 E9A2 D4F9 014E F11D  1DF7 DCA3 83BC 78E5 CD3A

Message to my public address may not be handled in a timely manner.
For a direct contact, please use my private address on my namecard.
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Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

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Re: Questions about XFS

[clflush]

>From what I know, and correct me if I'm wrong, XFS relies on the application 
side to do the right job but real world experience shows us that *a lot* of 
applications out there behave badly and cannot be trusted hence if something 
happens, XFS cannot "correct" the problem leaving you with headaches behind 
depending on how much data you lost/corrupted and the importance of it. IMHO, 
XFS *should* do some effort at assuring integrity to minimize the bad 
behavior of badly written applications out there. I know that XFS wasn't 
written for PC class hardware in the first place, but most people do not read 
enough to understand XFS and use it on their desktops/laptops because to be 
honest Linux doesn't really have a good file system, and XFS out of all 
available file systems, is the best in performance and scalability terms. 

On the one hand you have the old Ext3 FS which doesn't perform very well in 
many areas but IMO is a lot safer to work on (doesn't loose data that easily 
compared to XFS - and I'm talking from experience here because I use both 
file systems and I lost much more on the XFS system than on the Ext3 one) and 
on the other hand you have this excellent XFS file system with its clean 
layout and awesome performance + fancy features like GRIO, extents, allocate 
on flush, real time volumes, etc *but* is not "safe" enough to work with if 
you have unreliable hardware and/or a lot of power outage issues  - I've 
never lost data on Ext3 during a power outage but already lost 2 times data 
on XFS

Just my $0.02


On Thursday 15 March 2007 05:26:18 you wrote:
> From end-user's POV, this infamous XFS behavior is somewhat
> taken as XFS's inferiority compared to other filesystems.
> Even with "bad" applications (ex. firefox), this rarely happens
> on others, so regardless of what's on the FAQ, people logically
> concludes that the fault belongs to XFS anyway.
>
> So, what is the correct way to do IO?
> Is what firefox (and other bad apps) doing is so obvious(ly buggy),
> that it'll be acknowledged as a bug once reported? Or is it simply
> a mismatch between application expectation and XFS behavior,
> requiring a non-(obvious|generic) fix?
>
> Although I'm not a filesystem developer, I'm pretty impressed with
> XFS and willing to file a report/patch to those "buggy" apps if the
> issue is explainable to other app developers.
>
> >> was to press the reset button on the computer. After the reboot, when I
> >> opened Firefox again, I noticed that all my bookmarks were gone. Those
> >> bookmarks were imported from my desktop machine a few days after I
> >> configured the new server.
> >
> > This is a firefox bug - I've seen it before (on my mother's machine).
> >
> > It's due to firefox not doing the correct thing with IO on the bookmarks
> > file.

Re: Questions about XFS

[Geir A. Myrestrand]

clflush wrote:
> On the one hand you have the old Ext3 FS which doesn't perform very well in 
> many areas but IMO is a lot safer to work on (doesn't loose data that easily 
> compared to XFS - and I'm talking from experience here because I use both 
> file systems and I lost much more on the XFS system than on the Ext3 one) and 
> on the other hand you have this excellent XFS file system with its clean 
> layout and awesome performance + fancy features like GRIO, extents, allocate 
> on flush, real time volumes, etc *but* is not "safe" enough to work with if 
> you have unreliable hardware and/or a lot of power outage issues  - I've 
> never lost data on Ext3 during a power outage but already lost 2 times data 
> on XFS

You *always* use a UPS when you use XFS.
XFS does not prevent power outages [yet]...

> Just my $0.02

Save them for a UPS. ;-)

-- 

Geir A. Myrestrand

Re: Questions about XFS

[Martin Steigerwald]

Am Donnerstag 15 März 2007 schrieb clflush:
> From what I know, and correct me if I'm wrong, XFS relies on the
> application side to do the right job but real world experience shows us
> that *a lot* of applications out there behave badly and cannot be
> trusted hence if something happens, XFS cannot "correct" the problem
> leaving you with headaches behind depending on how much data you
> lost/corrupted and the importance of it. IMHO, XFS *should* do some
> effort at assuring integrity to minimize the bad behavior of badly
> written applications out there.

Hello,

as Eric wrote in this thread recent versions of XFS do an effort on 
avoiding these zeros in files:

"On the other hand, there were some changes made to xfs to explicitly 
sync files on close, if they have been truncated, which should help this 
sort of problem.  Depending on what's in OpenSuSE 10.2, that change may 
or may not be in your code..."

> On the one hand you have the old Ext3 FS which doesn't perform very
> well in many areas but IMO is a lot safer to work on (doesn't loose
> data that easily compared to XFS - and I'm talking from experience here
> because I use both file systems and I lost much more on the XFS system
> than on the Ext3 one) and on the other hand you have this excellent XFS
> file system with its clean layout and awesome performance + fancy
> features like GRIO, extents, allocate on flush, real time volumes, etc
> *but* is not "safe" enough to work with if you have unreliable hardware
> and/or a lot of power outage issues  - I've never lost data on Ext3
> during a power outage but already lost 2 times data on XFS

Since 2.6.17.7 and enabled write barriers I didn't loose meta data 
consistency on my laptop anymore and I can tell you that it crashed a lot 
due to my experiments with what not (especially OSS radeon drivers and 
beryl;-). I also had some classical power outages. I usually do not put a 
battery into my laptop if not needed.

And with recent XFS I did not encounter any data losses at all. Might have 
been luck, but before after a crash or power outage Akkregator told me 
sometimes that the file with the newsfeed stuff was corrupted and a 
backup has been restored. I didn't see this dialog since a long time on 
my laptop.

That given I would like to have more safety built into the filesystem 
itself, but at least current ext3 is too ancient technology for me. 
Coming from the Amiga a filesystem with a hard maximum number of inodes 
just doesn't fit my expectations (although original Amiga FFS has lot of 
shortcomings too;-).

The real challenge is to implement safety without serious loss of 
performance. You have more data safety in ext3, but less performance, and 
more performance in XFS, but potential less data safety with badly 
written applications. Not almost every bit of additional performance in 
XFS comes from transferring responsibility of data safety to the 
application, but I believe there is a relationship between safety and 
performance.

Maybe wandering logs / a log structured approach as (partly) seen in 
Reiser 4 and NetApp's WAFL might be a good approach to get more data 
safety without (much) less performance. (Well in the NetApp FAS non 
volatile RAM plays an important role, too.)

Regards,
-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7

Re: Questions about XFS

[Jason White]

On Fri, Mar 16, 2007 at 11:36:31AM +0100, Martin Steigerwald wrote:
 
> Since 2.6.17.7 and enabled write barriers I didn't loose meta data 
> consistency on my laptop anymore and I can tell you that it crashed a lot 
> due to my experiments with what not (especially OSS radeon drivers and 
> beryl;-). I also had some classical power outages. 

My laptop also supports write barriers, but I leave the battery in place in
case there's a power outage; effectively it's operating as a UPS.

This might be slightly off-topic, but in choosing a SATA drive for a desktop
machine, what features/standard-complaince should one look for in order to
ensure that write barriers work? I know this involves flushing the drive
cache, but is this support mandatory in any of the applicable standards?

cache flush support in SATA drives (was: Re: Questions about XFS)

[Martin Steigerwald]

Am Samstag 17 März 2007 schrieb Jason White:

> This might be slightly off-topic, but in choosing a SATA drive for a
> desktop machine, what features/standard-complaince should one look for
> in order to ensure that write barriers work? I know this involves
> flushing the drive cache, but is this support mandatory in any of the
> applicable standards?

Hello Jason!

I have no exact idea. I just now that dmesg usually tells you whether 
cache flushes are supported.

But shouldn't modern SATA drives support NCQ anyway? Since NCQ doesn't 
make any sense without the ability to flush the cache, I *think* any SATA 
drive with NCQ support should do. NCQ support would allow the block layer 
to offload the write barrier request ordering at least partly to the 
device firmware.

"ii. For devices which have queue depth greater than 1 but don't
support ordered tags, block layer ensures that the requests preceding
a barrier request finishes before issuing the barrier request.  Also,
it defers requests following the barrier until the barrier request is
finished.  Older SCSI controllers/drives and SATA drives fall in this
category."

(Documentation/block/barrier.txt of Linux Kernel 2.6.20.4)

This also indicates that SATA drives should support NCQ.

Regards,
-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7