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Date:      Wed, 04 Feb 2009 18:04:38 +0000
From:      Hugo Silva <hugo@barafranca.com>
To:        freebsd-questions@freebsd.org
Subject:   GEOM_JOURNAL on a 550G partition - opinions ?
Message-ID:  <4989D8B6.80505@barafranca.com>

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Hi list,

For a server I will be setting up, I am considering using gjournal on 
the partition that will hold all the www data.

The journaled partition (mounted async) would be mostly read from, 
uploads would not be very frequent and most sites wouldn't write to the 
disk. Logs would be kept elsewhere.

This server will have two hard disks, mirrored (gmirror) at the disk level.



Here are my questions:


- Will the fact that gmirror is underneath the journal 
(/dev/mirror/gm0s1f.journal) affect performance ? (either positively or 
negatively)
   (* I would be keeping the journal in the same provider)

- Would reads / writes be faster? considerably faster ? (gjournal) I've 
seen different numbers from different places, the impression I got is 
that reads should be faster while writes will be substantially slower - 
is this correct ?

- What about reliability ? From the manpage, I know that if I journaled 
the entire mirror, I would not need to sync it after an unclean shutdown.
   Going from the assumption that this will not be so for a single 
journaled partition, will there be any interference between gjournal and 
gmirror ?

- I've never had an UFS2 partition filled with more than 200G of data, 
so I am not sure what to expect for 550G with soft-updates (I expect 
this partition to hold close to 550G of data) - real numbers about this 
would also be helpful.


Any personal experiences concerning gjournal or gmirror+gjournal are 
greatly appreciated!

Thanks.

Hugo



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