EXT4에 쓰는 것이 디스크에 직접 쓰는 것보다 더 빠릅니까?

일부 SSD의 쓰기 속도를 테스트해 보았는데, 디스크에 직접 쓰는 것이 ext4로 포맷했을 때 디스크에 쓰는 것보다 느렸습니다. 어떻게 작동하나요? 이것이 맞는 걸까요, 아니면 제가 잘못 측정한 걸까요?

for i in {1..5}; do dd if=/dev/zero of=/dev/sda1 bs=1G count=1 oflag=dsync; done
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 7.18148 s, 150 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 7.18312 s, 149 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 7.1938 s, 149 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 7.15976 s, 150 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 7.2125 s, 149 MB/s

이제 디스크를 ext4로 포맷하면

mkfs.ext4 /dev/sda1
mount /dev/sda1 /tmp/test
mount -ls
/dev/sda1 on /tmp/test type ext4 (rw,relatime,data=ordered)

for i in {1..5}; do dd if=/dev/zero of=/tmp/test/test.txt bs=1G count=1 oflag=dsync; done
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 4.66437 s, 230 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 4.60112 s, 233 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 4.58899 s, 234 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 4.61334 s, 233 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 4.60241 s, 233 MB/s

감사해요

요하네스

편집: Frostschutz가 제안한 대로 /proc/sys/vm/block_dump를 활성화한 다음 ext4 드라이브에 복사하면 데이터가 커널에 의해 다르게 분할되는 것이 분명해집니다.

for i in {1..5}; do dd if=/dev/zero of=/tmp/test/test.txt bs=1G count=1 oflag=dsync; done
[  922.895200] dd(2571): READ block 74112 on unknown-block(8,0) (8 sectors)
[  922.903712] dd(2571): READ block 8448 on unknown-block(8,0) (8 sectors)
[  923.724470] dd(2571): dirtied inode 12 (test.txt) on sda
[  923.729762] dd(2571): dirtied inode 12 (test.txt) on sda
[  923.735005] dd(2571): dirtied inode 12 (test.txt) on sda
[  924.543323] kworker/u8:0(2560): READ block 8320 on unknown-block(8,0) (8 sectors)
[  924.553112] kworker/u8:0(2560): WRITE block 278528 on unknown-block(8,0) (2048 sectors)
[  924.561496] kworker/u8:0(2560): WRITE block 280576 on unknown-block(8,0) (2048 sectors)
[  924.570013] kworker/u8:0(2560): WRITE block 282624 on unknown-block(8,0) (2048 sectors)
[  924.578534] kworker/u8:0(2560): WRITE block 284672 on unknown-block(8,0) (2048 sectors)

for i in {1..5}; do dd if=/dev/zero of=/dev/sda bs=1G count=1 oflag=dsync; done
[ 1504.428021] kworker/u8:0(2560): WRITE block 0 on unknown-block(8,0) (8 sectors)
[ 1504.435320] kworker/u8:0(2560): WRITE block 8 on unknown-block(8,0) (8 sectors)
[ 1504.442589] kworker/u8:0(2560): WRITE block 16 on unknown-block(8,0) (8 sectors)
[ 1504.449955] kworker/u8:0(2560): WRITE block 24 on unknown-block(8,0) (8 sectors)
[ 1504.457342] kworker/u8:0(2560): WRITE block 32 on unknown-block(8,0) (8 sectors)
[ 1504.464720] kworker/u8:0(2560): WRITE block 40 on unknown-block(8,0) (8 sectors)