wow!

[Nicholas Steeves <nsteeves@gmail.com>]

Hi,

I upgraded to linux-4.2.3 and btrfs-progs-4.2.3 yesterday, and wow, 
there must have been bigger between linux-4.1.10 and 4.2.3 than were 
mentioned in the changelog!  I've been testing btrfs on a Thinkpad X200 
with an i5-2450M, Intel 320 SSD, and 8GB of RAM for over a year now, 
since when when linux-3.16 and btrfs-progs-3.17 were very new. 
Performance had been steadily degrading, or hit or miss (I'm not sure if 
defrag or fstrim actually work...), but stability was getting better.

The regular use case I use a benchmark is how fast the backup goes.  If 
the numbers seem unusual, I'll reboot and run:

tar cf- /.snapshots/only_one_snapshot | pv -pabet > /dev/null
then reboot and run
btrfs send /.snapshots/only_one_snapshot | pv -pabet > /dev/null

The worst run I've seen this last year for both of these commands~60 
MiB/s throughput to /dev/null...

A year ago, when the file system was brand new, after I filled the fs 
with my regular data, the average was:
GNU tar: ~125 MiB/s
BSD tar: ~129 MiB/s
btrfs send: ~140 MiB/s

Now with linux-4.2.3 and btrfs-progs-4.2.3:
GNU tar: ~134 MiB/s
BSD tar: ~129 MiB/s
btrfs send: ~133 MiB/s

This is the first time a backup has run at the speed of a fresh 
filesystem; I have not recently run fstrim or btrfs fi defrag, so I was 
very pleasantly surprised!  Thank you all very much for your hard work.

Kind regards,
Nicholas