From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Ahmed Kamal" Subject: Re: single disk reed solomon codes Date: Mon, 4 Aug 2008 09:52:50 +0300 Message-ID: <3da3b5b40808032352t704700cbmf99245fc56bfc2bd@mail.gmail.com> References: <3da3b5b40807190521x35477489sc06195bb182a4561@mail.gmail.com> <0cb201c8e9b2$a4272b20$0a00a8c0@ALDI2> <1216622923.6970.19.camel@s1.crocom.com.pl> <3da3b5b40807210040s72fdf458g44a1fe968088586e@mail.gmail.com> <7fe698080807210803h3a634eddw49be677e235c1c88@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 To: linux-btrfs@vger.kernel.org Return-path: In-Reply-To: <7fe698080807210803h3a634eddw49be677e235c1c88@mail.gmail.com> List-ID: An experiment of applying RS codes for protecting data, worth a look http://ttsiodras.googlepages.com/rsbep.html He overwrites a series of 127 sectors and still manages to correctly recover his data. We all know disks give us unreadable sectors every now and then, so at least on workstations/laptops this could really be useful ? Advantage over single-disk-raid1 is storage efficiency (4.2MB becomes 5.2MB), that means we get 80% of useable disk space, instead of 50% if I decide to raid1 everything ? On Mon, Jul 21, 2008 at 6:03 PM, Dongjun Shin wrote: > On Mon, Jul 21, 2008 at 4:40 PM, Ahmed Kamal > wrote: >> I definitely hope btrfs has this per-object "copies" property too. >> However, simply replicating the whole contents of a directory, wastes >> too much disk space, as opposed to RS codes >> > > Although adding redundancy mechanism will help increasing the integrity of data, > I'm not sure whether repeating the same kind of mechanism twice will help. > (AFAIK, RS is common in HDD and BCH is common in flash due to their own > physical characteristics) > > I think it is better to have another redundancy mechanism (like RAID1) > which is independent of the algorithm used by the underlying storage. > > -- > Dongjun >