Jim Dunham wrote: > Richard, > >> Ross wrote: >> >>> The problem is they might publish these numbers, but we really have >>> no way of controlling what number manufacturers will choose to use >>> in the future. >>> >>> If for some reason future 500GB drives all turn out to be slightly >>> smaller than the current ones you're going to be stuck. Reserving >>> 1-2% of space in exchange for greater flexibility in replacing >>> drives sounds like a good idea to me. As others have said, RAID >>> controllers have been doing this for long enough that even the very >>> basic models do it now, and I don't understand why such simple >>> features like this would be left out of ZFS. >>> >>> >>> >> I have added the following text to the best practices guide: >> >> * When a vdev is replaced, the size of the replacements vdev, measured >> by usable >> sectors, must be the same or greater than the vdev being replaced. >> This >> can be >> confusing when whole disks are used because different models of >> disks may >> provide a different number of usable sectors. For example, if a pool >> was >> created >> with a "500 GByte" drive and you need to replace it with another "500 >> GByte" >> drive, then you may not be able to do so if the drives are not of the >> same make, >> model, and firmware revision. Consider planning ahead and reserving >> some >> space >> by creating a slice which is smaller than the whole disk instead of >> the >> whole disk. >> > > Creating a slice, instead of using the whole disk, will cause ZFS to > not enable write-caching on the underlying device. >
Correct. Engineering trade-off. Since most folks don't read the manual, or the best practices guide, until after they've hit a problem, it is really just a CYA entry :-( BTW, I also added a quick link to CR 4852783, reduce pool capacity, which is the feature which has a good chance of making this point moot. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
