[Dovecot] Best filesystem?

[Ron Leach]

Stan Hoeppner wrote:

> Did you read
> the other excellent XFS resources available?
> 
> Users guide:
> http://xfs.org/docs/xfsdocs-xml-dev/XFS_User_Guide//tmp/en-US/html/index.html
> 
> File system structure:
> http://xfs.org/docs/xfsdocs-xml-dev/XFS_Filesystem_Structure//tmp/en-US/html/index.html
> 
> Training labs:
> http://xfs.org/docs/xfsdocs-xml-dev/XFS_Labs/tmp/en-US/html/index.html

I don't know why I missed these, thank you for pointing them out. 
Following Ted Tso's blog post mentioned by Timo, I'll read up on 
inodes and allocation so that I understand what is, and is not, 
committed, and when.  What I do worry about is a crash or power loss 
during the period between the time an application requests some data 
to be written, and the time that the filesystem actually completes 
writing it with all the file allocation data correct (and therefore 
tolerant of a crash from then on).

I thought I read in the XFS mount options something that suggested 
there was up to a 30 second window for this commit, which is a 
relatively long lump of time out of our UPS availability.  Here it is, 
not a mount option but a 'sysctl' (I expect these are discussed in the 
docs you pointed me to, above).

> git.kernel.org - linux/kernel/git/torvalds/linux-2.6.git/blob - Documentation/filesystems/xfs.txt
> 175         "fs.xfs.xfssyncd_centisecs     (Min: 100  Default: 3000  Max: 720000)
> 176         The interval at which the xfssyncd thread flushes metadata
> 177         out to disk.  This thread will flush log activity out, and
> 178         do some processing on unlinked inodes.
> 179 "

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/filesystems/xfs.txt;hb=HEAD

Why does this period in the UPS availability-time matter?  Because the 
UPS available-time has, of course, to first be allocated to the 
application machines to close their applications, before the file 
servers can be asked to 'commit' any delayed allocations and close 
down themselves (I don't want the file servers to close down while 
Dovecot (and any other applications) still have relevant data yet 
unwritten to the file-servers).

regards, Ron