file system journaling (was: Re: i-ram vs. tmpfs (was: Re: Mail clustering))
On [Fri, 13.04.2007 12:06], Anders Breindahl wrote:
AB> On 200704101607, Michael Loftis wrote:
AB> > RAID-5 is extremely slow at writes. Also can't forget about seeks.
AB> > Depending on your access patterns an external journal can be a definite
AB> > win, sometimes it's always a win with certain access patterns. EXT3 also
AB> > by default only journals metadata, not data, which means the write rate to
AB> > the journal is relatively low.
AB>
AB> Allow me to correct:
AB>
AB> Ext3 journals both data and metadata. Xfs only journals metadata. But
AB> that might be a relevant issue here, too, as many seem to prefer xfs on
AB> their mail servers.
no, that's not correct. ext3 can do both, jounral only metadata or
metadata+data, although i don't know what's the default.
see "man tune2fs":
-o [^]mount-option[,...]
journal_data
When the filesystem is mounted with journalling enabled, all data (not just metadata) is committed
into the journal prior to being written into the main filesystem.
journal_data_ordered
When the filesystem is mounted with journalling enabled, all data is forced directly out to the main
file system prior to its metadata being committed to the journal.
journal_data_writeback
When the filesystem is mounted with journalling enabled, data may be written into the main filesys-
tem after its metadata has been committed to the journal. This may increase throughput, however, it
may allow old data to appear in files after a crash and journal recovery.
greetz,
roman
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