BTRFS EXT3 EXT4 XFS and KVM virtual machine: a host-side filesystem comparison

Written by Gionatan Danti on . Posted in Linux & Unix

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Conclusions

Well, we are at the end. As said before, this article is a sort of experiment, as the testing methodology can surely be improved. If you have any idea, let me know it!

After having seen the results, we can say that you had to stay away from BTRFS in your KVM virtualizer host: this is not unexpected, as the KVM tuning page warns about very low BTRFS performance in these scenarios[3].

On the other hand, both EXT3/4 and XFS are more or less equivalent choices. The EXT-based filesystems have very good performance in both random and sequential tests, while XFS has an edge in the random write test and in fragmentation level.

Anyway, please remember that different kernel version can led to very different results, so things can always change in the future.

I hope that you find this article interesting. If you want, you can discuss it with me using the comment system or by writing at This email address is being protected from spambots. You need JavaScript enabled to view it.

Have a nice day!

 

References:

[1] - http://www.linux-kvm.org/page/Tuning_KVM

[2] - This email address is being protected from spambots. You need JavaScript enabled to view it./msg06595.html" target="_blank">http://www.mail-archive.com/This email address is being protected from spambots. You need JavaScript enabled to view it./msg06595.html

[3] - http://lwn.net/Articles/393148/

Comments   

 
#1 NGRhodes 2012-07-25 12:07
Hi,

When looking at fragmentation, do not forget that EXT4 supports a maximum 32K blocks in an extent, which at the default 4KB block size is 128MB.
As your benchmarks show, does not appear to be a performance limitation.
What would be more interesting is rerunning the benchmarks on an aged filesystem and compare how performance degrades with age.
 
 
#2 Gionatan Danti 2012-07-30 11:20
Hi NGRhodes,
sorry for the late reply.

You are correct about EXT4 extent size, but theoretically nothing prevents 2 extents to be placed one after the other. In fact, the filefrag utility checks if two extents are consecutively placed and, in this case, it does not report two different fragments, but only one.

Do you have any proposal about the aged filesystem? Any idea is welcomed ;)
 
 
#3 Jack Douglas 2012-10-14 21:15
Hi,

Thanks for the very helpful article. Would you be open to the suggestion of running the same tests with OCFS2 on a single node (it is the only fs other than btrfs with 'reflink' file snapshots that are very useful for backing up VMs)

Kind regards
Jack
 
 
#4 Boki 2016-04-21 12:59
Thanks for great article, and now, almost 4 years later, is there any new diff results or suggestions?
 

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