Quoth Marco Feichtinger <ma...@germteig.com>: > venti/mirrorarenas is undocumented, and I couldn't find any topic here, > which goes into more detail. > > So I am curious how does it work, > how does one to set it up, so the arenas get mirrored automatically, > and why do you use it instead of fs(3) mirror?
fs(3) can be used to mirror a _block device_. In principle, you can use this to mirror a full venti - or the arenas! - but you can also use it to mirror anything else, it doesn't care about the format of the data. venti/mirrorarenas should work to _update_ a mirror of an arenas partition: it mirrors _just_ the data log of the venti, and provides incremental backup. if you want it to be automatic, that's just a cron job; there's nothing fancy for it in venti itself. An important note is that, since it _only_ mirrors the arenas themselves, the destination is not a usable venti - for that, you'd need to build the index. In principle, if you keep the arena _separate_ from the indexes - i.e. on a different drive - this should allow for simply swapping which copy of the arenas is used _without updating the index_. There's also wrarena+rdarena. That needs to be used between _two instances of venti_ - i.e. the destination needs a full venti server, not just a disk - but has the advantage of allowing the data sets to not be _competely_ identical, and since it goes through the server, it ensures the index is up to date on the receiving end. There's a lot of different options on how to keep a venti system replicated / backed up, depending on the goal. For just backups, on one machine, where the entire venti is on one drive, fs(3) is probably the easiest approach - it can be configured to mirror venti across multiple drives, and the bootup scripts can automatically fall back to the mirror if the first drive fails. If the index is on a separate drive, though - e.g. index on SSD, data on HDDs - mirrorarenas can be used to keep the arenas in sync between multiple (sets of) HDDs, so that if one fails, venti can use the working drive while continuing to use the index on the SSD. Alternatively, for backing up _across the network_, scripts based on wrarena+rdarena are probably the way to go. This allows for mirroring between multiple separate ventis, even if the configuraiton of the arenas and indices are completely different. What to use and how to set it up depends, as always, on what you're trying to do :) - Noam Preil ------------------------------------------ 9fans: 9fans Permalink: https://9fans.topicbox.com/groups/9fans/Tca0eb0fbb2404e31-Mfca7d8f04716a17aa3283cc6 Delivery options: https://9fans.topicbox.com/groups/9fans/subscription
