UFS journal size

Matthew Seaman m.seaman at infracaninophile.co.uk
Wed Sep 21 10:41:25 UTC 2011

On 21/09/2011 10:48, Ross wrote:
> Quoting the manpage:
>          -s jsize  Specifies size of the journal if only one provider is
>                        used for both data and journal.  The default is one
>                        gigabyte.  Size should be chosen based on provider's
>                        load, and not on its size; recommended minimum is twice
>                        the size of the physical memory installed.  It is not
>                        recommended to use gjournal for small file systems
>                        (e.g.: only few gigabytes big).
> My question is: if I have 4 or 8 GB of RAM should I create 8 or even
> 16 GB journals?.. This seems huge especially if the fs size without
> journal is only 10 gigs. Or the recommended minimum is for systems low
> on RAM?

How much churn do you expect in the data on that partition?  A journal
that's about the same size as the actual filesystem in question and on
the same physical device is not really going to get you any advantages.
If it's mostly going to be read rather than written, then you wouldn't
fill up that size of journal in any case.

The 'twice physical RAM' advice is all about achieving maximum
performance on large filesystems with lots of data writes: if write
performance is not actually a limiting factor, then you could get away
with a much smaller or even no journal at all.

You might just as well use plain UFS+Softupdates.  Softupdates to
provide the meta-data ordering feature, so that if you do crash and need
to fsck the filesystem, there's not going to be any really nasty stuff
to fix.  Plain UFS because a filesystem of that size will take about as
long to fsck as it would to replay all the journalled but uncommitted



Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey     Ramsgate
JID: matthew at infracaninophile.co.uk               Kent, CT11 9PW

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