Date: Sun, 16 Oct 2011 11:30:03 -0700 From: Jeremy Chadwick <freebsd@jdc.parodius.com> To: "Luchesar V. ILIEV" <luchesar.iliev@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: [ZFS] Using SSD with partitions Message-ID: <20111016183003.GA29466@icarus.home.lan> In-Reply-To: <4E9B1C1E.7090804@gmail.com> References: <CACh33Fpz=uAp8h0Bjsi1Be=ob_94jXtN51mAHvGPkReY5MpTcg@mail.gmail.com> <4E9AE725.4040001@gmail.com> <169E82FD-3B61-4CAB-B067-D380D69CDED5@digsys.bg> <4E9B1C1E.7090804@gmail.com>
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On Sun, Oct 16, 2011 at 09:02:06PM +0300, Luchesar V. ILIEV wrote: > On 16/10/2011 19:17, Daniel Kalchev wrote: > > > > On Oct 16, 2011, at 17:16 , Luchesar V. ILIEV wrote: > > > >> 6. If, OTOH, you're running a reasonably recent -STABLE (8 or 9), > >> then your zpool version is likely 28 (thanks, pjd@), which means > >> ZIL is not that scary, but you might still lose some data. Even an > >> unexpected power failure might cause trouble, unless the SSD is > >> designed to handle it gracefully (this typically involves some sort > >> of capacitor). > > > > Just for the record: even without ZIL, you will most definitely lose > > data at power outage. In most cases, this will not damage the ZFS > > filesystem, but data will be lost. There is nothing that can prevent > > this. > > > > Therefore, with ZFS v28, adding ZIL does not introduce any more risk > > to your data. > > I might be wrong in my interpretation, but from what I remember, when > the power goes down, an unprotected SSD is likely to lose _more_ data > than simply its write buffers -- that's quite unlike a hard-drive. So > much, in fact, that the whole ZIL might become corrupted (and that's > potentially way more data than any device cache). > > _If_ that's true, then isn't an array of only "conventional" HDDs, where > the ZIL is interleaved with the zpool itself, at least a bit safer from > power failures? Again, if we are taking the cheaper SSDs into account. Please expand on the above, providing reference materials or links to things you've read that help shed light on all of this. More specifically: 1) I would like a definition of what "unprotected SSD" means and what a "protected SSD" is. 2) I would like an explanation as to what "SSDs are more likely than an MHDD to lose data on a power outage" means exactly (on a technical level, not something vague) and from where you got this interpretation. Thanks! -- | Jeremy Chadwick jdc at parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, US | | Making life hard for others since 1977. PGP 4BD6C0CB |
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