Craig Sanders <cas@taz.net.au> wrote:
On Mon, Jul 15, 2013 at 03:33:09PM +1000, Tim Connors wrote: [...]
Does anyone use zfs's dedup in practice? Completely useless.
yes, people do. it's very heavily used on virtualisation servers, where there are numerous almost-identical copies of the same VM with minor variations.
it's also useful on backup servers where you end up with dozens or hundreds of copies of the same files (esp. if you're backing up entire systems, including OS)
Are you actually talking about retroactive deduplication here, or just COW? IMHO taking a little extra care when copying VM images or taking backups and ensuring use of snapshots and/of --reflink are usually good enough as opposed to going back and hunting for duplicate data. [...]
Au contraire. If you use lvresize habitually, one day you're going to accidentally shrink your LV instead of expand it, and the filesystem below it will then start accessing beyond end of device, with predictably catastrophic results. Use lvextend prior to resize2fs, and resize2fs shrink prior to lvreduce, and you'll be right.
the risk of typing '-' rather than '+' does not scare me all that much.
That of course assumes you're using a relative size. If you're using an absolute size this is far less obvious. That's the other thing: lvextend -L 32G on a 64G LV will do nothing, as would lvreduce -L 64G on a 32G LV. This is useful when ensuring an LV meets minimum size requirements and saves significant (potentially buggy) testing code.
i tend to check and double-check potentially dangerous command lines before i hit enter, anyway.
craig
-- Sent from my phone. Please excuse my brevity. Regards, Matthew Cengia