New filesystem: Btrfs!

herbinator · n00b Joined: 14 Feb 2010 Posts: 3

I've got a strange issue with the spead of Btrfs (Kernel 2.6.32.7).

I used KVM and a qcow2-Image under ext4. Inside the Image a XP guest, normally booted in under 2 minutes. Now, on another, newer hard drive with Btrfs 0.19 it takes just over 10 minutes for the guest to be usable. Also copied the whole image once, no change.

Any ideas on how to remedy that situation or just switching back to ext4?

Dont Panic · Posted: Sun Feb 14, 2010 12:30 am Post subject:

The 2.6.33_rc process has been a busy time for Btrfs, and there are many improvements in the current rc release of the 2.6.33 kernel.

I'm not sure if any of these address your issue, but that should be the first thing you'd try.

I've had success simply backporting the 2.6.33 code to a 2.6.32 source tree, or you can try to build the latest 2.6.33 rc release.

herbinator · n00b Joined: 14 Feb 2010 Posts: 3

I tried the 2.6.33-RC-8, but it did not really changed anything at all for good. Any tweaks perhaps someone could try? The Wiki of btrfs seems kinda quiet about that and I am experiencing a CPU load > 10 just from reading that file (on an Intel i5 core).

devsk · Posted: Sun Feb 14, 2010 12:47 am Post subject:

herbinator · n00b Joined: 14 Feb 2010 Posts: 3

I am going to try that, thanks for the suggestion, never taken that into account so far, perhaps it is going to help.

Letharion · Veteran Joined: 13 Jun 2005 Posts: 1344 Location: Sweden

Since my workstation doesn't actually hold any critical data on it's own, I've upgraded it to btrfs on ssd. It's fast.

Letharion · Veteran Joined: 13 Jun 2005 Posts: 1344 Location: Sweden

If I turn compression on, what does it take to actually get files compressed? I'm guessing compression won't automagically happen on mount?
Will I need to move files to a different partition and back?

Dont Panic · Posted: Wed Feb 24, 2010 5:52 pm Post subject:

Dont Panic · Posted: Wed Feb 24, 2010 6:37 pm Post subject:

Up until now, I've always been consistent with my compression options once a volume was created. I've either always mounted it with compression, or always left compression off.

Based on Letharion's question, I decided to test what would happen if I swapped back and forth between mounting with compression enabled and disabled.

Surprisingly, Btrfs seemed to handle switching back and forth between compression enabled/disabled just fine, but I'm still not sure if it's wise, or if I'll do it on a regular basis myself.

Btrfs would not go back and compress files previously written with compression disabled. But Btrfs would compress files when mounted with compression even if previously mounted without compression. In my tests (using an md5sum to spot check some files), Btrfs would seamlessly handle files previously written with compression, when mounted as an uncompressed drive.

It's interesting to note that the 'du' command, and 'ls' command will show files sizes on an uncompressed basis, whether or not compression is enabled. To see how much space is being used, you need to use the 'df' command to differentiate between space used when comparing compression enabled/disabled.

Letharion · Veteran Joined: 13 Jun 2005 Posts: 1344 Location: Sweden

Adding compress to fstab will be the same as "-o compress", right?
I tried it anyway, and without being very scientific, I think I gained some space from tar-ing files together/apart.

On another note, it seems 33 is out, which makes me happy, running rc makes me nervous

More than running an experimental fs, which probably doesn't make sense

Dont Panic · Posted: Wed Feb 24, 2010 9:23 pm Post subject:

That should work. I might add many people are using 'compress-force' right now. It can actually be a little bit faster.

Here's my entry for my root partition:

BlueFusion · Guru Joined: 08 Mar 2006 Posts: 371

I'd only use compress-force if you're going to be storing small files on there. Well, maybe up to a few MB. If you are storing large files such as movies, stick with the compress option. The large files are going to waste alot of CPU time compressing, and not gain much space anyway. That is, unless they are RAW video files. Then I'd use compress-force.
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i7-940 2.93Ghz | ASUS P6T Deluxe (v.1) | 24GB Triple Channel RAM | nVidia GTX660
4x 4TB Seagate NAS HDD (Btrfs raid5) | 2x 120GB Samsung 850 EVO SSD (Btrfs raid1)

Letharion · Veteran Joined: 13 Jun 2005 Posts: 1344 Location: Sweden

I have installed btrfs-progs, and enabled btrfs support in the kernel. When I boot, I get

Shining Arcanine · Veteran Joined: 24 Sep 2009 Posts: 1110

fangorn · Veteran Joined: 31 Jul 2004 Posts: 1886

Hi,

I have a stupid little problem.

I used btrfs for trial on a backup drive. (I know: "Ha, Ha" Nelson Muns)

Now I would need the backup (harddisk died) and I can't mount the backup partition!

Letharion · Veteran Joined: 13 Jun 2005 Posts: 1344 Location: Sweden

Fangorn: Making really wild guesses here. Are you missing btrfs support in kernel? (Should give a different error IIRC) Is it an older btrfs format on the drive? Superblock may have gotten corrupted, try the mailing list.

Shining Arcanine; Ok, but where is the program supposed to come from? Which package? I don't have the program anywhere. Because I can't think of anything else, I'm gonna try just copying it from a different system later.

fangorn · Veteran Joined: 31 Jul 2004 Posts: 1886

I used the same kernel to format and firstly mount the device, so I doubt support is missing out of the blue. Using 2.6.32. The backup is quite fresh. :roll:

I don't know if an update of the btrfs-progs has happened in between.

But you remind me of something. I did an emerge -uD world the night before yesterday and did not run revdep-rebuild. Will try that this evening and see what happens.

Edit: AFAIK chkfs.xxx are either links to the filesystem specific tools of wrapper scripts to implement the standard answers. But I don't have one at hand atm.
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Letharion · Veteran Joined: 13 Jun 2005 Posts: 1344 Location: Sweden

Fangorn:
I dont think the format has changed since <2.6.31, so that shouldn't be it, but revdep can solve all kinds of strange issues, so try that

I notice that
1) I don't have a btrfs.fsck on a working btrfs install either...
2) You have a btrfsck in your post above. Maybe fsck.btrfs is expected to be linked to that? But then why don't I have that one the working system?

fangorn · Veteran Joined: 31 Jul 2004 Posts: 1886

I can't see how it is solved at my Gentoo box at home, but here with Debian fsck.xfs (don't have btrfs support at work

) is a script that if called by the init procedure, returns a defined value and if called on the command line echoes a message to use xfs_check and xfs_repair.

I can't say if btrfsck is capable of behaving correctly in the init procedure. So maybe it would be wise to NOT just link it to the fsck.btrfs :wink:

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Letharion · Veteran Joined: 13 Jun 2005 Posts: 1344 Location: Sweden

Shining Arcanine · Veteran Joined: 24 Sep 2009 Posts: 1110

Letharion · Veteran Joined: 13 Jun 2005 Posts: 1344 Location: Sweden

fangorn · Veteran Joined: 31 Jul 2004 Posts: 1886

There is hope for my backup.

According to this http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg04169.html btrfs does not behave well on external drives. To be precise, it cannot handle device name changes atm.

I was not aware of that. As I dynamically attach up to 5 drives as needed, this _might_ be a problem. :wink:

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Letharion · Veteran Joined: 13 Jun 2005 Posts: 1344 Location: Sweden

So, can external drives be given persistent names to solve this?