Date: Thu, 03 Oct 2013 18:20:32 +0200 From: Nikos Vassiliadis <nvass@gmx.com> To: Matthew Seaman <matthew@FreeBSD.org> Cc: freebsd-questions@freebsd.org Subject: zfs over geli over zfs (was: Re: zfs flag denoting unclean shutdown?) Message-ID: <524D9950.70400@gmx.com> In-Reply-To: <524C6259.9030609@FreeBSD.org> References: <524C3CF0.8050502@gmx.com> <524C6259.9030609@FreeBSD.org>
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On 10/02/2013 08:13 PM, Matthew Seaman wrote: > On 02/10/2013 16:34, Nikos Vassiliadis wrote: >> Is there a way to know if a zfs pool had an unclean shutdown? >> An attribute or maybe something during mount time similar to what ufs >> does (WARNING: / was not properly dismounted)? > > Other than looking at the system logs for evidence of an abnormal > shutdown, no. (Absence of anything in the logs is pretty good evidence > for the system falling over pretty hard... Usually something to do with > the power being turned off.) > > However, due to the design of ZFS unclean shutdowns like this are > nowhere near as problematic as on UFS. Basically, you're guaranteed > that what is written on disk is always consistent. You might lose a few > transactions -- essentially the last few seconds of file system activity > -- but that doesn't usually make a great deal of difference after the > system reboots again. Oh, yeah -- absolutely no time will be needed to > be spent cleaning and repairing filesystems: with ZFS, reboot after > crash is as fast as a normal reboot. Thanks Matthew, I realized I should have used a more appropriate subject. I'll explain what my actual goal is:) I am after a really specific use-case and the last minute transactions are important. Using a zpool over geli over a zvol. I'd like to know if during shutdown the kernel flushes all zfs files caches in order so these last minutes transactions won't be lost. The unmounting order is far from obvious (zfs over geli over zfs) and i wonder if such a scheme will succeed. I can't afford losing the last transactions of my home dir every time i shutdown my laptop;) The obvious solution is to create two slices and dedicate a slice to geli. Like this: mypool lives on slice1 myencpool lives on slice2.eli I am after this: mypool lives on slice1 myencpool lives on /dev/zvol/mypool/avolume.eli The second scheme will allow me to have an encypted home and not to pre-allocate space. A quick test showed that it might work... On the other hand conceptually seems like a very bad idea haha. I think I've heard people doing this zfs over geli over zfs before... Thanks for any thoughts, Nikos
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