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Re: RaiserFS via NFS

On Sun, 18 Apr 2004 02:51, Dan MacNeil <omacneil@brave.cs.uml.edu> wrote:
> I've just converted from mbox to maildir
> Right now there are some users with 500 files in a directory, I expect
> this go grow.
> I expect this figure to grow. RaiserFS is looking good.

ReiserFS is very good for maildir.  For Maildir storage the average file size 
is often in the 10K-20K range, this means that there are a few megabyte+ 
files and many <4K files.  ReiserFS uses a 4K block size, and for a file <16K 
in ReiserFS the last part of the file (known as the "tail") will be stored in 
a block with tails of other files.  So for example you could have 4*900 byte 
files in one 4K block.  This can significantly decrease disk space, for a 
Maildir system that will be close to 2K per file.

The reduction in disk space will however come at the cost of increased CPU 
use, so if your CPU is slow then you may want to mount -o notails.  But with 
the way CPUs have been getting faster that shouldn't be a problem.

> The benefits of running a central storage server and a bunch of seperate
> web/smtp/pop3/spamfiltering/ftp/ servers, one storage server running not
> much more than NFS all connected with a cheap Gigbit switch are also
> appealing to me.
> Is there any benefit to RaiserFS if I am accessing it via NFS ?

Some years ago I did some Bonnie++ file creation tests on an AIX machine and 
found that a ReiserFS file system NFS mounted over 10baseT outperformed the 
local disk!  Yes, ReiserFS offers definite benefits even over NFS.  But in 
2.6.x Ext3 uses directory hashing which significantly improves performance 
with many files in a directory, ReiserFS is no longer 30 times faster than 
Ext3 for file creation, maybe 4-5 times faster.

But the NFS store is probably a bad idea.  NFS isn't something you want to use 
for reliability.  I suggest having some spamfiltering machines on the 
front-end which also direct the mail to the correct back-end server.  Have 
POP, IMAP, and SMTP for delivery running on the machines with the mail store.  
Have webmail on entirely separate machines.  Have LDAP servers to contain 
user-names, passwords, and the record of which server stores each user's 

I've run a system like this with >200,000 mail boxes per server (Dell 2650 
machines with 4G of RAM and 4 SCSI disks in a RAID-5 array).

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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