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Re: How efficient is mounting /usr ro?

On Wed, 26 Nov 2003 14:24, Bernd Eckenfels 
<ecki@calista.eckenfels.6bone.ka-ip.net> wrote:
> > 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.
> I guess the thread was about non-journalling filesystems beeing faster, and
> less of a risk if used ro.

Even for a non-journalling file system there should be no risk.  If a file 
system is mounted and never written to then only a single disk block should 
change, the one with the dirty bit indicating that an fsck might be needed on 
a reboot.  If that block is corrupted then you may need to use the backup 
superblock in the worst-case, but that would require a crash while mounting 
the file system.

> > 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.
> News Servers are even worth. And full-filesystem scans and some backup
> tools make the a-time less usefull anyway.

There should be a way of reading a file without changing the ATIME that backup 
programs can use.

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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