From 30e266c11686b3d5855e7b69f0612f01f130b4cd Mon Sep 17 00:00:00 2001 From: Alex Elsayed Date: Thu, 1 Mar 2018 17:48:47 -0800 Subject: So long tiering; hello disk groups and targets --- index.mdwn | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) (limited to 'index.mdwn') diff --git a/index.mdwn b/index.mdwn index d750c8b..d89ba70 100644 --- a/index.mdwn +++ b/index.mdwn @@ -56,9 +56,16 @@ format and mount a single device with the default options, run: For a multi device filesystem, with sda1 caching sdb1: - bcachefs format /dev/sda1 --tier=1 /dev/sdb1 + bcachefs format /dev/sd[ab]1 \ + --foreground_target /dev/sda1 \ + --promote-target /dev/sda1 \ + --background_target /dev/sdb1 mount -t bcachefs /dev/sda1:/dev/sdb1 /mnt +This will configure the filesystem so that writes will be buffered to /dev/sda1 +before being written back to /dev/sdb1 in the background, and that hot data +will be promoted to /dev/sda1 for faster access. + See `bcachefs format --help` for more options. ## Documentation @@ -104,11 +111,13 @@ necessary, but I'm not expecting any more incompatible disk format changes. - Tiering/writeback caching: - Bcachefs allows you to assign devices to different tiers - the faster tier - will effectively be used as a writeback cache for the slower tier, and - metadata will be pinned in the faster tier. + Bcachefs allows you to specify disks (or groups thereof) to be used for + three categories of I/O: foreground, background, and promote. Foreground + devices accept writes, whose data is copied to background devices + asynchronously, and the hot subset of which is copied to the promote devices + for performance. - Basic tiering functionality works, but it's not (yet) as configurable as + Basic caching functionality works, but it's not (yet) as configurable as bcache's caching (e.g. you can't specify writethrough caching). - Replication -- cgit v1.2.3