> [ ... ] It is hard for me to see a speed issue here with
> Btrfs: for comparison I have done a simple test with a both a
> 3+1 MD RAID5 set with a 256KiB chunk size and a single block
> device on "contemporary" 1T/2TB drives, capable of sequential
> transfer rates of 150-190MB/s: [ ... ]
The figures after this are a bit on the low side because I
realized looking at 'vmstat' that the source block device 'sda6'
was being a bottleneck, as the host has only 8GiB instead of the
16GiB I misremembered, and also 'sda' is a relatively slow flash
SSD that reads are most at around 220MB/s. So I have redone the
simple tests with a transfer size of 3GB, which ensures that
all reads are from memory cache:
with compression:
soft# mount -t btrfs -o commit=10,compress-force=zlib /dev/md/test5
/mnt/test5
soft# mount -t btrfs -o commit=10,compress-force=zlib /dev/sdg3 /mnt/sdg3
soft# rm -f /mnt/test5/testfile /mnt/sdg3/testfile
soft# /usr/bin/time dd iflag=fullblock if=/dev/sda6 of=/mnt/test5/testfile
bs=1M count=3000 conv=fsync
3000+0 records in
3000+0 records out
3145728000 bytes (3.1 GB) copied, 15.8869 s, 198 MB/s
0.00user 2.80system 0:15.88elapsed 17%CPU (0avgtext+0avgdata 3056maxresident)k
0inputs+6148256outputs (0major+346minor)pagefaults 0swaps
soft# /usr/bin/time dd iflag=fullblock if=/dev/sda6 of=/mnt/sdg3/testfile
bs=1M count=3000 conv=fsync
3000+0 records in
3000+0 records out
3145728000 bytes (3.1 GB) copied, 16.9663 s, 185 MB/s
0.00user 2.61system 0:16.96elapsed 15%CPU (0avgtext+0avgdata 3056maxresident)k
0inputs+6144672outputs (0major+346minor)pagefaults 0swaps
soft# btrfs fi df /mnt/test5/ | grep Data
Data, single: total=3.00GiB, used=2.28GiB
soft# btrfs fi df /mnt/sdg3 | grep Data
Data, single: total=3.00GiB, used=2.28GiB
soft# filefrag /mnt/test5/testfile /mnt/sdg3/testfile
/mnt/test5/testfile: 8811 extents found
/mnt/sdg3/testfile: 8759 extents found
Slightly weird that with a 3GB size the number of extents is
almost double that for the 10GB, but I guess that depends on
speed.
Then without compression:
soft# mount -t btrfs -o commit=10 /dev/md/test5 /mnt/test5
soft# mount -t btrfs -o commit=10 /dev/sdg3 /mnt/sdg3
soft# rm -f /mnt/test5/testfile /mnt/sdg3/testfile
soft# /usr/bin/time dd iflag=fullblock if=/dev/sda6 of=/mnt/test5/testfile
bs=1M count=3000 conv=fsync
3000+0 records in
3000+0 records out
3145728000 bytes (3.1 GB) copied, 8.06841 s, 390 MB/s
0.00user 3.90system 0:08.80elapsed 44%CPU (0avgtext+0avgdata 2880maxresident)k
0inputs+6153856outputs (0major+345minor)pagefaults 0swaps
soft# /usr/bin/time dd iflag=fullblock if=/dev/sda6 of=/mnt/sdg3/testfile
bs=1M count=3000 conv=fsync
3000+0 records in
3000+0 records out
3145728000 bytes (3.1 GB) copied, 30.215 s, 104 MB/s
0.00user 4.82system 0:30.93elapsed 15%CPU (0avgtext+0avgdata 2888maxresident)k
0inputs+6152128outputs (0major+347minor)pagefaults 0swaps
soft# filefrag /mnt/test5/testfile /mnt/sdg3/testfile
/mnt/test5/testfile: 5 extents found
/mnt/sdg3/testfile: 3 extents found
Also added:
soft# rm -f /mnt/test5/testfile /mnt/sdg3/testfile
soft# /usr/bin/time dd iflag=fullblock if=/dev/sda6 bs=128k count=3000 | dd
iflag=fullblock of=/mnt/test5/testfile bs=128k oflag=sync
3000+0 records in
3000+0 records out
393216000 bytes (393 MB) copied, 160.315 s, 2.5 MB/s
0.02user 0.46system 2:40.31elapsed 0%CPU (0avgtext+0avgdata 1992maxresident)k
0inputs+0outputs (0major+124minor)pagefaults 0swaps
3000+0 records in
3000+0 records out
393216000 bytes (393 MB) copied, 160.365 s, 2.5 MB/s
soft# /usr/bin/time dd iflag=fullblock if=/dev/sda6 bs=128k count=3000 | dd
iflag=fullblock of=/mnt/sdg3/testfile bs=128k oflag=sync
3000+0 records in
3000+0 records out
393216000 bytes (393 MB) copied, 113.51 s, 3.5 MB/s
0.02user 0.56system 1:53.51elapsed 0%CPU (0avgtext+0avgdata 2156maxresident)k
0inputs+0outputs (0major+120minor)pagefaults 0swaps
3000+0 records in
3000+0 records out
393216000 bytes (393 MB) copied, 113.544 s, 3.5 MB/s
soft# filefrag /mnt/test5/testfile /mnt/sdg3/testfile
/mnt/test5/testfile: 1 extent found
/mnt/sdg3/testfile: 22 extents found
soft# rm -f /mnt/test5/testfile /mnt/sdg3/testfile
soft# /usr/bin/time dd iflag=fullblock if=/dev/sda6 bs=1M count=1000 | dd
iflag=fullblock of=/mnt/test5/testfile bs=1M oflag=sync
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 68.5037 s, 15.3 MB/s
0.00user 1.16system 1:08.50elapsed 1%CPU (0avgtext+0avgdata 2888maxresident)k
0inputs+0outputs (0major+347minor)pagefaults 0swaps
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 68.5859 s, 15.3 MB/s
soft# /usr/bin/time dd iflag=fullblock if=/dev/sda6 bs=1M count=1000 | dd
iflag=fullblock of=/mnt/sdg3/testfile bs=1M oflag=sync
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 56.6714 s, 18.5 MB/s
0.00user 1.21system 0:56.67elapsed 2%CPU (0avgtext+0avgdata 3056maxresident)k
0inputs+0outputs (0major+345minor)pagefaults 0swaps
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 56.7116 s, 18.5 MB/s
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