Date: Sun, 3 Nov 2013 08:32:03 -0700 (MST) From: Warren Block <wblock@wonkity.com> To: symbolics@gmx.com Cc: geom@freebsd.org, hackers@freebsd.org Subject: Re: GEOM mentor request Message-ID: <alpine.BSF.2.00.1311030801540.38648@wonkity.com> In-Reply-To: <20131103090323.GA1744@lemon> References: <20131101103158.GA35397@lemon> <alpine.BSF.2.00.1311011310340.23437@wonkity.com> <20131103090323.GA1744@lemon>
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On Sun, 3 Nov 2013, symbolics@gmx.com wrote: > On Fri, Nov 01, 2013 at 01:23:12PM -0600, Warren Block wrote: >> On Fri, 1 Nov 2013, symbolics@gmx.com wrote: >> >>> + Implement new things. Some ideas I have had: >>> + GEOM "ERASE" - Rewrite deletes into random writes. >>> + GEOM "PLUG" - Persistent version of the connect/disconnect verbs >>> where the flag sits in the class metadata. This might be a cleaner >>> approach, rather than adding the verbs to all the existing >>> providers. >>> + GEOM "TAP" - Allow userspace processes to hook into the GEOM >>> API. Intended for debugging and development. >>> + GEOM "WCACHE" - Allow you to use small, fast provider as a buffer >>> for a larger, slower provider. >>> + GEOM DTrace provider. Provide GEOM specific probes to complement >>> the IO provider. >>> + Probably other bits I can't remember right now. >> >> How about an explicit geom retaste command? "true > /dev/ada0" is >> misleading to the reader. > > Yes, that would be good. It's on my list. > >> Also, a RAM-cached version of gmirror that would report writes finished >> as soon as the faster drive finishes. Kind of the opposite of the >> WCACHE above. This would permit creating mirrors of an SSD and hard >> drive without performance loss, at least up until available write >> buffer space runs out. This one may not be so easy. > > I can see the benefit. This would be like a mirror with a journal. As > long as it has a different name from mirror, 'lazy mirror' ?, I think it > would be interesting. The only concern I have would be that some users > could use it and assume the normal mirror semantics, e.g. that all discs > are equally redundant, which wouldn't be true. I've been calling it a "slow" mirror. Come to think of it, that's a little misleading. "Async mirror"? There may be an existing term. As pointed out, it's probably non-trivial to implement. The WCACHE you suggest above (the Linux guys have "bcache") is probably more benefit to more people.
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