Date: Tue, 31 Aug 2010 04:09:04 -0700 From: Carl <k0802647@telus.net> To: freebsd-fs@freebsd.org Subject: gjournal alignment on 4K sector advanced format drives Message-ID: <4C7CE2D0.40400@telus.net>
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My understanding is that I can avoid misalignment-induced performance problems with Western Digital WDxxEARS drives (4KiB physical sector size) by ensuring two things: 1. GPT partitions are aligned to 4KiB boundaries, and 2. Use "newfs -b 32768 -f 4096 ..." so that UFS2 fragments are not smaller than the physical sector size. True? Now I want to add gjournal to some of my partitions. It seems to me that I must also ensure the journal is aligned just as I've done with the data. So far, though, I have found no information as to how the journal's own filesystem layout works. Does it use fixed size blocks/fragments like the UFS2 data does? If so, what is its minimum addressable unit size? If it is smaller than 4KiB, we get journal misalignment and a performance loss, right? What must I do to ensure the journal is fully aligned? In the past I've put the data and journal on the same provider, but I am unsure whether a specified size for the journal is accurately observed. If I specify a 1GiB journal, will I get exactly that? My concern is whether an added/subtracted sector might be used for some kind of journal header, thereby throwing off the alignment of the journal again. Is it better to put the journal on its own provider (ie. separate partition) to aid alignment in some way? What are the pros and cons for shared vs. separate providers in general? Carl / K0802647
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