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Re: How efficient is mounting /usr ro?

On Wed, 26 Nov 2003 07:45, Chema <chema.news.gmane@zarco.cjb.net> wrote:
> RC> Why would you get better performance?  If you mount noatime then
> RC> there's no writes to a file system that is accessed in a read-only
> RC> fashion and there should not be any performance issue.
> Hum, ¿are you talking only about ext3?  'Couse I don't think the reading

I am talking about any file system.  When only reading from a file system 
there should not be any performance difference when comparing a RO mount vs a 
NOATIME mount.  If there is a difference then it's a bug in the file system.

> performance of ext2 and reiserfs/jfs/whatever will be the same just by
> freezing the access time.

Of course different file systems give different performance characteristics, I 
know this well, I wrote one of the two benchmarks used in the URL you cite.

> ext3 is just a
> somewhat dirty hack on ext2, and without journaling their performance would
> be probably the same.

My point is that for read-only operations ext2 and the original ext3 should 
give the same performance.

Incidentally if you want significantly better performance for such things then 
you want to run 2.6.0 or a Red Hat kernel so you get directory hashing on 
ext3.  It appears from a casual code inspection that 2.6.0-test10 does not 
support directory hashing for ext2.  So in 2.6.0-test10 ext3 should 
significantly outperform ext2 when there are large numbers of files in a 
directory.  I'll have to do some benchmarks on this.

> Now, how much difference really makes noatime??

The difference it makes is that reading from the disk will never cause disk 
writes.  If you access large numbers of files or if you have IO hardware that 
has a bottleneck of write bandwidth (EG a typical mail server) then NOATIME 
makes a significant difference.

> Also, access time is usually a piece of information I'll like to keep. 

In which case you need to mount RW and your entire arguement is bogus.

http://www.coker.com.au/selinux/   My NSA Security Enhanced Linux packages
http://www.coker.com.au/bonnie++/  Bonnie++ hard drive benchmark
http://www.coker.com.au/postal/    Postal SMTP/POP benchmark
http://www.coker.com.au/~russell/  My home page

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