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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Random read / write speed

Operating systems often issue many small, random I/O operations. This is even more true when you put many OS onto one single server. In this case, random I/O speed become a crucial parameter. How well the contenders fare in this workload?

First, random read:

BTRFS EXT3 EXT4 XFS with KVM: Random read

As you can see, while BTRFS is the slowest again, it is not so much behind the others. EXT3, EXT4 and XFS are again basically tied.

Now, random write:

BTRFS EXT3 EXT4 XFS with KVM: Random write

We see a very different picture now: BTRFS is way, way slower then the others. EXT3 and EXT4 are tied, with XFS showing a great score when dealing with low queue dept (the usual case). On the other hand, when dealing with higher queue dept (a not so common scenario on guest virtual machines), XFS slow down considerably, even falling slightly behind EXT3/4.


#1 NGRhodes 2012-07-25 12:07

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

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
#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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