Date: Wed, 20 Jul 2016 11:45:03 -0700 From: Maxim Sobolev <sobomax@freebsd.org> To: Kirk McKusick <mckusick@mckusick.com>, FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Optimizing UFS 1/2 for non-rotating / compressed storage Message-ID: <CAH7qZftBGgajT2=_A4nGbNJB%2B2Tj1km8Z%2BDtrt4AKAoAyjo%2BRQ@mail.gmail.com>
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Hi Kirk et al, Do you by any chance have some hints of what parameters we need to set in newfs to maximally fit the following criteria: 1. Minimize free space fragmentation, i.e. we start with huge array or zeroes, we want to end up with as few number of continuous zero areas as possible (i.e. minimize free space discontinuity). 2. Blocks that belong to the same file should be as continuous as possible "on disk". 3. Each individual file should preferably start at the block offset that is multiple of certain pre-defined power-of-two size from the start of partition, e.g. 64k, 128k etc. The file system in question is write-mostly. We create image from scratch every time and them populate with installworld + pkg add. Any free space is subsequently erased with dd if=/dev/zero of=/myfs/bigfile; rm /myfs/bigfile, unmounted and image is compressed. We also grossly over-provision space, i.e. 2GB UFS image is created, less than 1GB is used at the end. Any hints would be appreciated. Thanks! -Maxim
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