On Apr 2, 2010, at 2:05 PM, Edward Ned Harvey 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.
If the HBA is configured for RAID mode, then it will reserve some space on disk for its metadata. This occurs no matter what type of disk you attach. > There is some question about performance. Is there any additional overhead > caused by using a slice instead of the whole physical device? No. > 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? If the disk is only used for ZFS, then it is ok to enable volatile disk write caching if the disk also supports write cache flush requests. If the disk is shared with UFS, then it is not ok to enable volatile disk write caching. -- richard > 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. > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss ZFS storage and performance consulting at http://www.RichardElling.com ZFS training on deduplication, NexentaStor, and NAS performance Las Vegas, April 29-30, 2010 http://nexenta-vegas.eventbrite.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
