Usable Union Filesystems?

Enverex · 2012-07-31 12:29:59

I'm in a situation where I'd like to union my drives simply to make accessing their content easier from other applications. i.e. I don't want to have to add multiple "sources" to applications, such as "Music 1", "Music 2" etc and some applications don't even allow adding of more than one source (or destination, depending what I'm doing) so this is quite often a necessity.

I'm avoiding RAID because I'd like to be able to add and remove drives with little hassle, plus if one drive dies, I'd rather not lose everything, at least in this setup I only lose what's on the single drive, not all drives (Mirrored RAID isn't an option due to cost and the fact I would need far more drive bays than I have).

Anyway, with that out of the way, what options do people see as viable at the moment? I'm having trouble finding even a single one as they all seem very poorly supported. I would have thought this was something people used quite often as it seems like a highly useful feature to have.

AUFS3 needs a custom built kernel, so I'd rather avoid that (I'm trying to keep the system as vanilla as possible).

mhddfs looked ideal but the performance is dire, as shown below from my tests earlier:

URandom (Fuse, Real)
204800000 bytes (205 MB) copied, 92.3259 s, 2.2 MB/s
204800000 bytes (205 MB) copied, 32.0806 s, 6.4 MB/s

Zero (Fuse, Real)
204800000 bytes (205 MB) copied, 16.8018 s, 12.2 MB/s
204800000 bytes (205 MB) copied, 1.62708 s, 126 MB/s

So what other options do I have? If someone knows of some other idea that would also fulfil the requirements I'm looking for, please voice it.

Wilco · 2012-07-31 13:49:56

You probably want unionfs

I've used AUFS in the past but after some updates I switched to unionfs and it's even easier to setup and use. If I remember correctly I only had to setup fstab and after that four different disk directories are now all mapped to one central directory.

Enverex · 2012-07-31 13:59:47

Isn't UnionFS also FUSE based though? I'd assume that because of that, it's going to perform just as well (or rather, as bad as) mhddfs. That said, I'll try it anyway and let you know how I get on.

Enverex · 2012-08-01 09:13:03

Wilco wrote:

You probably want unionfs
I've used AUFS in the past but after some updates I switched to unionfs and it's even easier to setup and use. If I remember correctly I only had to setup fstab and after that four different disk directories are now all mapped to one central directory.

Looks like UnionFS is just as bad.

Direct Disk
100000+0 records in
100000+0 records out
204800000 bytes (205 MB) copied, 1.74819 s, 117 MB/s

UnionFS
100000+0 records in
100000+0 records out
204800000 bytes (205 MB) copied, 13.3022 s, 15.4 MB/s

So both FUSE implementations result in roughly 1/10th the performance of using the disk without the FUSE layer. That's an obscene performance loss.

Does anyone know of any others or any special trick to avoiding this performance penalty?

Gusar · 2012-08-01 09:22:38

AUFS isn't FUSE based. And neither is unionfs, though I think there's also a FUSE version.

You'll have to get over the "don't want to compile my own kernel" thing and go with AUFS.

Enverex · 2012-08-01 10:07:26

Gusar wrote:

AUFS isn't FUSE based. And neither is unionfs, though I think there's also a FUSE version.
You'll have to get over the "don't want to compile my own kernel" thing and go with AUFS.

I can only find a FUSE version of UnionFS in the repos/AUR which gave the impression it's the only really usable version. I'll test AUFS to see what performance is like.

Enverex · 2012-08-13 08:10:46

Bringing this back to life for a related question. AUFS3 has been working fine but I've run into a problem. One of the drives has filled up, but it's overflowing to the next drive in the list or doing any form of branch balancing. Wikipedia (erk) claims that AUFS supports this, but I've not seen any mention or information in support of this anywhere else.

Anyone know how to use branch balancing on AUFS, if it does indeed support it?

detto · 2012-08-29 11:20:23

Interesting thread!
I'm also looking for a solution as I plan to set up a storage pool for all my media data like pictures, music, videos and documents.

The first solutions I stumbled upon were:
Drobo
RAID 1
RAID 5
RAID 0 , JBOD
Windows 8 Storage Spaces

NONE of these are exactly what I'm looking for though.
All of these work pretty much the same in the regard for what I'm looking forward to. They all cost too much, waste too much hdd space and/or are unsafe (JBOD, RAID 0, Windows 8 Storage Spaces without Redundancy).

So, after weeks of searching I found that the only solutions seem to exist in the UNIX world, well hello again my old friend ArchLinux!
Now I heard of UnionFS, Union Mount, AUFS and MHDDFS. THere are probably more?
I haven't installed my ArchLinux yet but would like to know which is "the best".
Music, pictures, videos and documents would all land on one big pool and would be used in programs like Banshee and XBMC. Pretty much my media HDD station or HTPC.

Filling up one drive after another is also useful for simpler backups. That way I'd only have to care about one single drive that needs to be mirrored and that's it.
I'm still wondering why all the world is using RAID and whatnot when there are probably so much better solutions out there. Of course I now have to test HOW good those really are, but hope is there at least.

Would be nice to see what your following findings are Enverex.

Enverex · 2012-08-29 11:27:32

AUFS seems to be the best, it has no performance hit that I can see and is configurable to work in lots of different ways.
The downside with AUFS is that you need to use the AUFS friendly kernel in AUR or the "linux-pf" kernel, also in AUR.

Any that run in userspace (i.e. FUSE) rather than kernel have MASSIVE performance hits.

SanskritFritz · 2012-08-29 12:06:57

Nobody mentioned LVM yet. Maybe I don't see something obvious as the reason for it, but for me it looks like the solution, since you can install any filesystem onto an LVM partition.

ehlo · 2012-08-29 16:56:16

If you're happy to have one music folder with subfolders such as Music1, Music2 inside it then you could consider bind mounts?

detto · 2012-08-30 14:16:04

@SanskritFritz: I'd have to take a look at LVM and see if it fulfills the need. Is there any good documentation available that you're aware of?

@ehlo: Subfolders is not an option for me, it's the same as symlinking folders to another place.
The goal is to have a extendable storage pool that consists of independent hard drives. In that pool overlapping folders (hdd1/music, hdd2/music,..) get merged.

SanskritFritz · 2012-08-30 14:40:47

detto wrote:

@SanskritFritz: I'd have to take a look at LVM and see if it fulfills the need. Is there any good documentation available that you're aware of?

Well, I just took the wiki, it explains it very well: https://wiki.archlinux.org/index.php/Lvm

detto · 2012-08-30 15:48:04

And here comes another contender
http://code.google.com/p/sfs/

Enverex · 2012-09-01 18:20:16

LVM can't easily have a disk pulled out and accessed separately afaik, I remember reading up on it and it had a lot of similar issues to RAID when it came to disks dying and having to undergo work to get everything back in order again.

detto wrote:

And here comes another contender
http://code.google.com/p/sfs/

Also ruled out for the reason I ruled the others out:

SFS is built on top of FUSE (the "filesystem in userspace" layer).

Anything that runs in userspace will have -crippling- performance.

detto · 2012-09-02 08:41:49

I have the same feeling about it. LVM was no option back in the time, it sounded too complicated and was not that easy like a mhddfs for example.
Of course, I prefer a solution without FUSE too.
As far as I know, that would only be AUFS for now?

Enverex · 2012-09-02 11:02:29

That's my finding so far, unfortunately (wouldn't be a pain if it didn't require a custom kernel).

progandy · 2012-09-02 11:07:43

Enverex wrote:

That's my finding so far, unfortunately (wouldn't be a pain if it didn't require a custom kernel).

If you find some people who share your needs you coud set up a common build server and a repository.
Edit: Linux-pf includes aufs3 among other patches and has a repository

Last edited by progandy (2012-09-02 11:11:06)

Enverex · 2012-09-02 12:22:56

Yeah, that's what I'm using. By custom kernel I simply meant "not the stock Arch one".

detto · 2012-09-03 17:39:54

I found overlayfs today, it's in the Ubuntu kernel I guess?

But it's hard to find any info about it. Still don't know wether it allows to overlay just one directory over another, or if it can handle multiple (more than 2) directories.

Gusar · 2012-09-03 17:50:41

Overlayfs is extremely simple. It's literally what the name says - one filesystem laid on top of another. And the "lower" filesystem is always read-only. As such it doesn't meet the needs you guys here have. That's why I didn't mention it. The primary use of it are livecd/liveusb distros.

If you're interested anyway, the upstream code is here: http://git.kernel.org/?p=linux/kernel/g … ;a=summary <- v13 is for kernel 3.4; v14 is for kernel 3.6. For kernel 3.5, you'll need to get patches from the Ubuntu kernel - I have a link for that too somewhere, I can search for it if someone wants.

Last edited by Gusar (2012-09-03 17:54:07)

detto · 2012-09-03 18:05:49

That's a bummer.

Well then still aufs3 or mhddfs for me. Can't believe we have 2012 and no other practical solution exists to this.

Enverex · 2012-09-03 22:53:46

detto wrote:

That's a bummer.
Well then still aufs3 or mhddfs for me. Can't believe we have 2012 and no other practical solution exists to this.

It's actually gone backwards, these things used to be better supported. Strange really.

Gusar · 2012-09-04 00:13:58

Enverex wrote:

It's actually gone backwards, these things used to be better supported.

When? UnionFS and AUFS were always external patches, union-mount has been in development since forever and is still not complete, overlayfs is relatively new.

Or are you referring to the fact that AUFS used to be part of the Arch kernel a long time ago? It was a pain in the butt (new kernels couldn't be released because the devs would need to wait for AUFS to get updated), and also went against the Arch policy of sticking as close as possible to upstream.

The thing is, I don't really see the big deal about needing to compile your own kernel.

Lynden · 2012-09-04 13:59:52

You could try ZFS, the module version, not the FUSE one.
http://zfsonlinux.org

I'm not sure how stable it is though.

Arch Linux

#1 2012-07-31 12:29:59

Usable Union Filesystems?

#2 2012-07-31 13:49:56

Re: Usable Union Filesystems?

#3 2012-07-31 13:59:47

Re: Usable Union Filesystems?

#4 2012-08-01 09:13:03

Re: Usable Union Filesystems?

#5 2012-08-01 09:22:38

Re: Usable Union Filesystems?

#6 2012-08-01 10:07:26

Re: Usable Union Filesystems?

#7 2012-08-13 08:10:46

Re: Usable Union Filesystems?

#8 2012-08-29 11:20:23

Re: Usable Union Filesystems?

#9 2012-08-29 11:27:32

Re: Usable Union Filesystems?

#10 2012-08-29 12:06:57

Re: Usable Union Filesystems?

#11 2012-08-29 16:56:16

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#12 2012-08-30 14:16:04

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#13 2012-08-30 14:40:47

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#14 2012-08-30 15:48:04

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#15 2012-09-01 18:20:16

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#16 2012-09-02 08:41:49

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#17 2012-09-02 11:02:29

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#18 2012-09-02 11:07:43

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#19 2012-09-02 12:22:56

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#20 2012-09-03 17:39:54

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#21 2012-09-03 17:50:41

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#22 2012-09-03 18:05:49

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#23 2012-09-03 22:53:46

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#24 2012-09-04 00:13:58

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#25 2012-09-04 13:59:52

Re: Usable Union Filesystems?

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