Slower write with ZIL on SSD

[tuaris]

I thought adding the ZIL to a dedicated SSD would improve write speed, but instead it reduces it slightly.

With ZIL

Code: Select all

/usr/bin/time -h dd if=/dev/zero of=sometestfile bs=1024 count=1604800
1604800+0 records in
1604800+0 records out
1643315200 bytes transferred in 39.472788 secs (41631597 bytes/sec)
        40.60s real             0.39s user              16.62s sys

Without ZIL

Code: Select all

/usr/bin/time -h dd if=/dev/zero of=sometestfile bs=1024 count=1604800
1604800+0 records in
1604800+0 records out
1643315200 bytes transferred in 24.981995 secs (65779982 bytes/sec)
        24.99s real             0.44s user              14.79s sys

Is that usually the case? The system I have is a P4 3.2 GHz and 4GB of RAM.

[b0ssman]

zil only speeds up synchronous writes.

your dd command is not synchronous

[tuaris]

zil only speeds up synchronous writes.

your dd command is not synchronous

Interesting, could you explain more or show me were I can find more information about this?

[crowi]

a good start is here:
http://www.solarisinternals.com/wiki/in ... ices_Guide