abysmal rm performance?
Quoted 4 lines
You /really/ need to read up on the btrfs wiki.
The short answer is yes, btrfs does a LOT more metadata processing due to the checksumming it does by default.
According to the wiki, checksumming has barely any influence, so I guess the above advice is not really helpful?
https://btrfs.wiki.kernel.org/index.php/Mount_options
nodatasum
(...)
On most modern CPUs this option does not result in any reasonable performance improvement.
Quoted 8 lines
Then there's the whole problem that you didn't provide nearly enough information about your test to tell what it was actually comparing. What sort of raid1, btrfs/md/dm/hardware/what, and if btrfs raid1, was that for both data and metadata or just one of the two and what was the other one if they weren't both raid1? And if you were testing btrfs raid1, what did you do with the ext4 test to try to make it comparable since ext4 doesn't have a native raid1 mode, or was it on a single device?
ext4: using md RAID
btrfs:
Data, RAID1: total=1.73TB, used=1.36TB
System, RAID1: total=32.00MB, used=264.00KB
System: total=4.00MB, used=0.00
Metadata, RAID1: total=79.00GB, used=70.23GB
Quite high metadata usage here.
The filesystems on ext4 and btrfs are copies; there are >30 milion inodes on ext4; most of the files have multiple hardlinks.
So paraphrasing my question: is there anything to improve "rm" performance with btrfs?
"nodatacow" might help a bit, but then, it disabled the compression, which is a major drawback.
Signature · 2 lines
Tomasz Chmielewski http://wpkg.org
Tomasz Chmielewski posted on Mon, 22 Jul 2013 12:22:11 +0700 as excerpted:
Quoted 5 lines
Quoted 4 lines
You /really/ need to read up on the btrfs wiki.
The short answer is yes, btrfs does a LOT more metadata processing due to the checksumming it does by default.
Quoted 8 lines
According to the wiki, checksumming has barely any influence, so I guess the above advice is not really helpful?
https://btrfs.wiki.kernel.org/index.php/Mount_options
nodatasum (...) On most modern CPUs this option does not result in any reasonable performance improvement.
It's worth noting that in the context of the full description, that's referencing data write performance as that's where the checksumming would be done and the CPU performance would matter, not really delete performance, where the bottleneck is likely to be the storage device seek times.
However, being a user not a btrfs dev, and not having actually tested it, what I do NOT know is whether that option disables just the calculation, so the same seeks would be done and the same "unmetadata" (given the file was written with nodatasum) would be erased in any case, or if it short circuits the entire process.
It might be worth some benchmarks to see...
Quoted 8 lines
btrfs:
Data, RAID1: total=1.73TB, used=1.36TB System, RAID1: total=32.00MB, used=264.00KB System: total=4.00MB, used=0.00 Metadata, RAID1:
total=79.00GB, used=70.23GBQuite high metadata usage here.
Yes. It's worth noting, however, that btrfs does store small files directly in the inode metadata itself, rather than in separate data extents. So that can be considered too and may be part of it.
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The filesystems on ext4 and btrfs are copies; there are >30 milion inodes on ext4; most of the files have multiple hardlinks.
Hardlinks: Until recently btrfs has problems if there were too many hardlinks in a directory. They fixed that, but if you're doing a LOT of hardlinking, it may well be that is playing some part, as I don't know how performant the new code is. It may be worth reading the list archives on that topic.
Quoted 5 lines
So paraphrasing my question: is there anything to improve "rm" performance with btrfs?
"nodatacow" might help a bit, but then, it disabled the compression, which is a major drawback.
I have a strong suspicion nobarrier may help quite a bit with high-number delete loads, tho of course it DOES come with data corruption risks in the event of a power failure.
It's also likely that as the actual number of bugs go down as they are beginning to now, and the devs focus more on performance tuning, that this will get better.
Other than that, and of course the hardware/ssd option (I'm using btrfs in btrfs raid1 mode on a pair of ssds here and the zero-seek-time DOES make a difference, but I'm not doing terabytes of data either; that's still on reiserfs on spinning rust, here), it may simply be that btrfs isn't a filesystem choice well matched to your needs.
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Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman