Date: Fri, 25 Feb 2011 12:07:11 +0100 From: Terje Elde <terje@elde.net> To: freebsd-questions@freebsd.org Subject: GELI reliability Message-ID: <0847F66E-F541-4604-8238-A869CCDEE163@elde.net>
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Hi, I'm curious about GELIs theoretical behavior when faced with errors, and = also any experience anyone might have. As an example, if I run ZFS with raidz over X drives, then the zpool = should have no issue surviving the complete loss of a full disk. Also, = the familiar "FAILURE - READ_DMA" or READ_DMA48 errors from a disk = having a bad day should also be no issue, certainly not an issue that = would result in crash, or worse still, loss of data. What I'm wondering is how much worse off the data would be if I were to = slide inn a GELI layer between the physical drives, and the zpool. That is, if I use GELI directly on the individual drives ( /dev/ada0, = /dev/ada1 etc), then make a raidz pool on top of the .eli devices ( = /dev/ada0.eli, /dev/ada1.eli etc). For READ_DMA type errors, I suppose GELI could just forward the same = errors up the stack, and that'd be that, the errors wouldn't be any more = severe than what I'd have anyway? One exception could be if GELI sector size is larger than disk sector = size. Not being too familiar with GELIs internal workings, I'm not sure = that has to be the case though. GELI sectors have a new IV pr. sector, = but the crypto itself is still done in 128 or 256 bit blocks, so given a = single faulty disk sector, the rest of the GELI sector could still be = read and decrypted? Or are entire GELI sectors faulted if a (smaller) = underlaying sector is unreadable? And finally, what if an entire drive dies a cruel and horribly death, = all of it's data returning to the large bit bucket in the sky? Would = GELI simply relay the same errors upstack to ZFS, so ZFS would be able = to handle it as well as it would have without GELI? I've used ZFS over GELI in the past, but never had any hardware issues = to see how it plays out. I'm considering deploying it for more stuff now, and reliability wise, = from what I know, I could loose very little by using GELI, or it could = be time to buy napkins, because the risk of a grown man crying while = trying to mop up spilled bits from the floor is increased significantly. (backups should avoid the need for tears though, besides, I don't have a = mop) Terje
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