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Lockheed

Member

Registered: 2010-03-16

Posts: 1,521

BTRFS performance degradation on SSD

I am experiencing massive performance degradation on my BTRFS root/home partition.

Except for regular daily updates, nothing changed in the system. The mount point remained the same

UUID=541ccaf2-4d4e-4a18-a7c1-66dc246a634b /  btrfs rw,noatime,compress=lzo,ssd,space_cache,autodefrag 0 0

but the performance dropped to less than 8% of norm.

Before:

# dd if=tempfile of=/dev/null bs=1M count=1024
+600 MB/s
 (can't remember the exact value)

Now:

# dd if=tempfile of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 26.4373 s, 40.6 MB/s

I created an ext4 partition on the same SSD and it is not being affected:

# dd if=/mnt/usb/tempfile of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 4.15292 s, 259 MB/s

I also tested a 5400rpm Sata II HDD with btrfs data partition - looks unaffected:

/mnt/Disk_D  btrfs rw,noatime,compress=zlib,autodefrag,nofail 0 0

# dd if=/mnt/Disk_D/tempfile of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 2.91769 s, 368 MB/s

It seemed pointless because hdd was unaffected, but just to be sure, I tried downgrading kernel to 3.12 - the problem persists.
Same goes for mount options like  ssd,space_cache,autodefrag.

I'd appreciate some suggestions.

Last edited by Lockheed (2014-03-08 09:56:44)

frostschutz

Member

Registered: 2013-11-15

Posts: 1,419

Re: BTRFS performance degradation on SSD

No SSD reads at 600MB/s. Chances are you've benchmarked memory cache before...

40MB/s is still ridiculous. Unless it's USB2.

What's autodefrag? You don't defrag SSD.

Lockheed

Member

Registered: 2010-03-16

Posts: 1,521

Re: BTRFS performance degradation on SSD

Is is an SSD on SATA II interface, so theoretically its limit is at 250MB/s, but with btrfs compression I used to get ~600MB/s with this very test.

This set of mount options (including autodefrag)  I arrived to after a lengthy discussion about optimal SSD mount options on the btrfs mailing list.