Date: Wed, 11 Nov 2009 17:06:38 +0100 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-geom@freebsd.org Subject: Re: gjournal and calculation of the size of journal provider Message-ID: <hdenee$1sm$2@ger.gmane.org> In-Reply-To: <4AFADF4A.80404@quip.cz> References: <4AF84245.7070108@quip.cz> <hdbf04$21k$1@ger.gmane.org> <4AFADF4A.80404@quip.cz>
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Miroslav Lachman wrote: > Ivan Voras wrote: >> Miroslav Lachman wrote: >>> What is the right rule for journal size calculation? >>> There are two sources stating different things. >>> >>> 1] journal size depends on disk write speed >>> http://lists.freebsd.org/pipermail/freebsd-fs/2006-June/002016.html >>> >>> "For example your disk can write >>> at 60MB/s. Journal switch time is 10 seconds. The journal provider has >>> to have place to keep two journals (active and inactive). So bascially >>> you need 60*10*2MB + gjournal headers." >>> >>> >>> 2] journal size depends on RAM size >>> http://www.freebsd.org/doc/en/articles/gjournal-desktop/article.html#UNDERSTANDING-JOURNALING >>> >>> >>> >>> "Your RAM size should fit in 30% of the journal provider's space. For >>> example, if your system has 1 GB RAM, create an approximately 3.3 GB >>> journal provider. (Multiply your RAM size with 3.3 to obtain the size >>> of the journal)." >>> >>> >>> What's the right size for journal on 143GB 15k rpm SAS disks on >>> machine with 16GB of RAM? Based on second case, it will be more than >>> 50 GB - one third of the size of disk. This is insane vasting. >> >> It really does depend on the speed of drives but it could be >> approximated by saying there will not be more data to write than the >> size of memory (which is probably wrong since you can write from >> /dev/zero indefinitely). The first advice is sufficient, but you should >> probably extend the result by 20% to be safer. > > > So is it safe to use 4GB on PERC6 array, which is capable of 150MB/s > write speed by dd test? > dd if=/dev/zero of=/dev/mfid0s2e bs=1m count=10000 > > (150 * 10 * 2 * 1.2) = 3600 > > 150 is write speed in MB/s > 10 is journal switch time > 2 is active + inactive journal > 1.2 is +20% to base safer This looks fine! > And next question about journal. I saw following message in log after > reboot: > > GEOM_JOURNAL: Journal 1933335573: mfid0s2d contains journal. > GEOM_JOURNAL: Journal 1933335573: mfid0s2e contains data. > GEOM_JOURNAL: Journal mfid0s2e clean. > GEOM_JOURNAL: BIO_FLUSH not supported by mfid0s2d. > GEOM_JOURNAL: BIO_FLUSH not supported by mfid0s2e. > > "BIO_FLUSH not supported" - is it OK to use gjournal on top of the Dell > PERC (LSI MegaRAID) with battery backup unit? I think so, but rather ask > somebody... :) I think you are safe if the controller has the BBU working and enabled.
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