Ext3 resizing and performance

[Felipe Alfaro Solana]

On 12/10/06, Gabriel Dragffy <dragffy at yandex.ru> wrote:
> Now I am in the Ext3 territory I do have a couple of things that I'd
> like to clear up.
>
> Firstly I am unsure about the -T flag with news, largefile, largefile2
> being options, which should I choose for best performance on / ?

This options control different aspects of the filesystem, like the
total number of i-nodes of the filesystem. "news" usage is intended
for a filesystem wil lots of small files (one i-node per 4KB so, for
4GB volume, you'll get 1M i-nodes). "largefile" is intended for
filesystems with less and larger files than "news"  (one i-node per
1MB, so for a 4GB volume you will get 4096 i-nodes) . "largefile4" is
intended for filesystems with few and very lage files (one i-node per
4MB, so for a 4GB volume you will get 1024 i-nodes).

The "-T" flag thus provides simple ways of controlling the number of
i-nodes of the filesystem. For more fine-grained contro, you can use
-N (numer of i-nodes) or -i (ratio of bytes per i-node).

> More importantly is how do you grow a logical volume ONLINE, without
> first unmounting it when it is using Ext3?

You can use ext2online. However, ext2online has some limitations that
resize2fs don't. For most of the typical use, ext2online will do fine,
however.

> What does the "commit" function actually do? I have changed it from 5
> seconds to 600 on my laptop - will that affect something adversely?

If my memory serves me well, it dictates the amount of time pdflush
uses to look through the list of dirty blocks in order to write them
back to disk. The longest the interval, the longest it will time for
pdflush to write dirty buffers to disk, increasing the disk of data
loss due to power outages and making the disk idle for longer time.

> I recently changed all my LVs from ReiserFS to Ext3 formats. I can't
> believe the difference - about 20% increase in performance. GIMP now
> starts in 5 seconds instead of 7 after the computer being freshly
> rebooted. On the whole the computer seems to do a whole lot less
> scratching when firing up applications. I can't say that ReiserFS was
> fragmented, I had a standard desktop install and it was freshly
> installed just 3 weeks ago.
>
> Before changing to Ext3 I gave JFS a whirl and found it to be sllooww.
> Copying a large file took 6 mins as opposed to 4 on Reiser. And just
> starting the computer or applications would result in more-than-required
> HDD thrashing - obviously not a good filesystem for the computer and
> quite perhaps easily fragmented.

I find XFS to be extremely fast, but I have suffered some problems in
the past and I wouldn't recommend it for critical environments.