On May 24, 2012, at 3:38 PM, Bruce Dubbs wrote:
> The fstab now looks like:
>
> /dev/sdc1 / ext4 noatime,discard,data=writeback 1 1
> /dev/sda3 swap swap pri=1 0 0
> /dev/sda1 /boot ext3 defaults 1 2
> /dev/sda9 /usr/src ext3 defaults 1 2
> /dev/sda11 /home ext3 defaults 1 2
> /dev/sdb5 /var ext3 defaults 1 2
> /dev/sdb6 /tmp ext3 defaults 1 2
>
> I don't think putting /boot on the ssd would make much of a difference.
> From the time I hit enter in grub to the time the kernel messages
> start is a second or less.
Are you booting from sdc (i.e., BIOS is booting from sdc)?
IDK what the rest of your setup is, but IIRC, I can get to login
(after BIOS POST, etc) in about a second.
> I then did a benchmark on rsync without the make check. When building
> on /tmp, the CMMI time was 20 seconds. When I changed the build to /mnt
> (on the ssd) the build time was 7.9 seconds.
>
> Not bad.
Interesting data, but it might be a bit misleading to attribute all
the speedups to the SSD:
1) /tmp is ext3
2) /tmp is mounted with kernel defaults (relatime?)
3) / is mounted with data=writeback
1. Ext3 is probably far worse than ext4 for CMMI tasks. Ext4 is
faster on file creation, and if it's used without barriers is going
to be much faster on writes. Obviously the tradeoff is there is
filesystem safety.
2. Mounted with defaults, I'd guess that ext3 is probably using
relatime. This is better than with atime enabled, but probably far
worse than noatime. IIRC, relatime still writes atime, but just less
frequently. It's still not as good as noatime. Here's a casual
write-up (with references to the epic war on LKML):
http://tinyurl.com/2exlv7u
3. That same article quotes Torvalds, IIRC, in a heated LKML on
the noatime issue:
"But yeah, 'noatime,data=writeback' will quite likely be
*quite* noticeable (with different effects for different
loads), but almost nobody actually runs that way."
I think the context was about filesystem safety. On a dev machine,
ext4 without barriers and data=writeback obviously makes sense. But,
it's not something I'd suggest for anyone who is concerned about the
data on the drive.
Overall, I think the results would be more robust if you could run
the same test with ext3 with the same mount options, and see what
those results are.
Q
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