On Mar 9, 2011, at 1:46 PM, Chris Murphy wrote: > > > On Mar 9, 2011, at 1:35 PM, objectwerks inc wrote: > >>>> The integrity of the data with files after any issues such as these may be >>>> suspect, especially if the fileystem was on a RAID5 which is very well >>>> known for silent data corruption. This is why RAID5 should not be used. >>> >>> OK that's possibly a whole separate thread for qualifying such a statement. >>> Apple has a supported product that uses RAID 5. I have clients with them >>> and they've lost drives, and no data, and no data corruption. And an even >>> larger sample size exists if filesystems other than jhfs+ are considered. >>> RAID 5/6 are common with ext3, ext4, XFS and other file systems without >>> anyone suggesting RAID 5 in particular is known for itself increasing the >>> incidence of silent data corruption. >>> >> >> >> There is a reason why it is called silent data corruption. They may not >> know they have it. It happens all the time and with HW raid 5 you may not >> even know it for a long time. >> >> This is the whole reason why ZFS was made. > > ZFS was not made for combating this claim of RAID 5 specific silent data > corruption, but rather silent data corruption in general.
And the difference is? You corrupt one disk in a RAID 5 array and the whole array is corrupted. > > RAID 5 employs parity. RAID 1 does not, nor do conventional non-arrayed jhfs+ > volumes. While RAID parity is not as sophisticated at ZFS checksumming, it is > certainly better than nothing. So there is some error detection and > correction possible, so I'm not understanding how RAID 5 is "well known for > silent data corruption" and should not be used. I think this is a rather > remarkable claim. > > > Chris Murphy If you have one disk that has silent data corruption (and parity may not help you at all as you calculate your new parity on the corrupted data) you compound it with RAID 5. http://www.raidinc.com/pdf/Silent%20Data%20Corruption%20Whitepaper.pdf http://boink.superatomic.com/2009/04/25/the-raid-5-write-hole/ http://www.google.com/#hl=en&sugexp=ldymls&xhr=t&q=raid+5+silent+data+corruption&cp=24&qe=cmFpZCA1IHNpbGVudCBjb3JydXB0aW9u&qesig=0VyEUZb1ePVXqTxPyJd8vg&pkc=AFgZ2tkTDI1HqM7fc6R1egXasC-1CNF3wT4BG5rzsZmDlr4IGBRuaMW3LWOqaaHzeI1IQlVZ2T5WTE3o3LlGRR6gLiYOy2lsHA&pf=p&sclient=psy&site=&source=hp&aq=0b&aqi=&aql=&oq=raid+5+silent+corruption&pbx=1&bav=on.2,or.&fp=ef34c9a9ed856910 _______________________________________________ MacOSX-admin mailing list [email protected] http://www.omnigroup.com/mailman/listinfo/macosx-admin
