On 2017年09月24日 21:24, Fuhrmann, Carsten wrote:
Hello,
i run a few performance tests comparing mdadm, hardware raid and the btrfs
raid. I noticed that the performance for small blocksizes (2k) is very bad on
SSD in general and on HDD for sequential writing.
2K is smaller than the minimal btrfs sectorsize (4K for x86 family).
It's common that unaligned access will impact performance, but we need
more info about your test cases, including:
1) How write is done?
Buffered? DIO? O_SYNC? fdatasync?
I can't read Germany so I'm not sure what the result means. (Although
I can guess Y axle is latency, but I don't know the meaning of X axle.
And how many files are involved, how large of these files and etc.
2) Data/meta/sys profiles
All RADI1?
3) Mkfs profile
Like nodesize if not default, and any incompat features enabled.
I wonder about that result, because you say on the wiki that btrfs is very
effective for small files.
It can be space effective or performance effective.
If *ignoring* meta profile, btrfs is space-effectient since it inline
the data into metadata, avoiding padding it to sectorsize so it can save
some space.
And such behavior can also be somewhat performance effective, by
avoiding extra seeking for data, since when reading out the metadata we
have already read out the inlined data.
But such efficiency come with cost.
One obvious one is when we need to convert inline data into regular one.
It may cause extra tree balancing and increase latency.
Would you please try retest with "-o max_inline=0" mount option to
disable inline data (which makes btrfs behavior like ext*/xfs) to see if
it's related?
Thanks,
Qu
I attached my results from raid 1 random write HDD (rH1), SSD (rS1) and from
sequential write HDD (sH1), SSD (sS1)
Hopefully you have an explanation for that.
raid@raid-PowerEdge-T630:~$ uname -a
Linux raid-PowerEdge-T630 4.10.0-33-generic #37~16.04.1-Ubuntu SMP Fri Aug 11
14:07:24 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
raid@raid-PowerEdge-T630:~$ btrfs --version
btrfs-progs v4.4
best regards
Carsten
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