On Fri, Apr 2, 2010 at 4:05 PM, Edward Ned Harvey <guacam...@nedharvey.com>wrote:
> Momentarily, I will begin scouring the omniscient interweb for > information, but I’d like to know a little bit of what people would say > here. The question is to slice, or not to slice, disks before using them in > a zpool. > > > > One reason to slice comes from recent personal experience. One disk of a > mirror dies. Replaced under contract with an identical disk. Same model > number, same firmware. Yet when it’s plugged into the system, for an > unknown reason, it appears 0.001 Gb smaller than the old disk, and therefore > unable to attach and un-degrade the mirror. It seems logical this problem > could have been avoided if the device added to the pool originally had been > a slice somewhat smaller than the whole physical device. Say, a slice of > 28G out of the 29G physical disk. Because later when I get the > infinitesimally smaller disk, I can always slice 28G out of it to use as the > mirror device. > > > > There is some question about performance. Is there any additional overhead > caused by using a slice instead of the whole physical device? > > > > There is another question about performance. One of my colleagues said he > saw some literature on the internet somewhere, saying ZFS behaves > differently for slices than it does on physical devices, because it doesn’t > assume it has exclusive access to that physical device, and therefore caches > or buffers differently … or something like that. > > > > Any other pros/cons people can think of? > > > > And finally, if anyone has experience doing this, and process > recommendations? That is … My next task is to go read documentation again, > to refresh my memory from years ago, about the difference between “format,” > “partition,” “label,” “fdisk,” because those terms don’t have the same > meaning that they do in other OSes… And I don’t know clearly right now, > which one(s) I want to do, in order to create the large slice of my disks. > > Your experience is exactly why I suggested ZFS start doing some "right sizing" if you will. Chop off a bit from the end of any disk so that we're guaranteed to be able to replace drives from different manufacturers. The excuse being "no reason to, Sun drives are always of identical size". If your drives did indeed come from Sun, their response is clearly not true. Regardless, I guess I still think it should be done. Figure out what the greatest variation we've seen from drives that are supposedly of the exact same size, and chop it off the end of every disk. I'm betting it's no more than 1GB, and probably less than that. When we're talking about a 2TB drive, I'm willing to give up a gig to be guaranteed I won't have any issues when it comes time to swap it out. --Tim --Tim
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