Ulrich, in his e-mail Robert mentioned _two_ things regarding ZFS: [1] ability to detect errors (checksums) [2] using ZFS didn't caused data lost so far I completely agree that [1] is wonderful and this is huge advantage. And you also underlined [1] in you e-mail ! The _only_ thing I mentioned is [2]. And I guess Robert wrote about it only because ZFS is relatively young. When you talk about VxFS/UFS you don't underline that they don't lose data - it would be ridiculous.
Regards przemol On Fri, Dec 22, 2006 at 11:39:44AM +0100, Ulrich Graef wrote: > [EMAIL PROTECTED] wrote: > > >Robert, > > > >I don't understand why not loosing any data is an advantage of ZFS. > >No filesystem should lose any data. It is like saying that an advantage > >of football player is that he/she plays football (he/she should do that !) > >or an advantage of chef is that he/she cooks (he/she should do that !). > >Every filesystem should _save_ our data, not lose it. > > > > > yes, you are right: every filesystem should save the data. > (... and every program should have no error! ;-) > > Unfortunately there are some cases, where the disks lose data, > these cannot be detected by traditional filesystems but with ZFS: > > * bit rot: some bits on the disk gets flipped (~ 1 in 10^11) > (cosmic rays, static particles in airflow, random thermodynamics) > * phantom writes: a disk 'forgets' to write data (~ 1 in 10^8) > (positioning errors, disk firmware errors, ...) > * misdirected reads/writes: disk writes to the wrong position (~ 1 > in 10^8) > (disks use very small structures, head can move after positioning) > * errors on the data transfer connection > > You can look up the probabilities at several disk vendors, the are > published. > Traditional filesystems do not check the data they read. You get strange > effects > when the filesystem code runs with wrong metadata (worst case: panic). > If you use the wrong data in your applicaton, you 'only' have the wrong > results... > > ZFS on the contrary checks every block it reads and is able to find the > mirror > or reconstruct the data in a raidz config. > Therefore ZFS uses only valid data and is able to repair the data blocks > automatically. > This is not possible in a traditional filesystem/volume manager > configuration. > > You may say, you never heard of a disk losing data; but you have heard > of systems, > which behave strange and a re-installation fixed everything. > Or some data have gone bad and you have to recover from backup. > > It may be, that this was one of these cases. > Our service encounters a number of these cases every year, > where the customer was not able to re-install or did not want to restore > his data, > which can be traced back to such a disk error. > These are always nasty problems and it gets nastier, because customers > have more and more data and there is a trend to save money on backup/restore > infrastructures which make it hurt to restore data. > > Regards, > > Ulrich > > -- > | Ulrich Graef, Senior Consultant, OS Ambassador \ > | Operating Systems, Performance \ Platform Technology \ > | Mail: [EMAIL PROTECTED] \ Global Systems Enginering \ > | Phone: +49 6103 752 359 \ Sun Microsystems Inc \ > ---------------------------------------------------------------------- Jestes kierowca? To poczytaj! >>> http://link.interia.pl/f199e _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
