From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: Split RAID: Proposal for archival RAID using incremental batch checksum Date: Wed, 17 Dec 2014 08:49:21 +1100 Message-ID: <20141217084921.360ca442@notabene.brown> References: <20141029200501.1f01269d@notabene.brown> <20141103165217.3bfd3d3e@notabene.brown> <20141125095052.51f8eadc@notabene.brown> <20141202084611.45f56d6a@notabene.brown> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/pXxQc7fhuBvi6RUVNC+qW_Q"; protocol="application/pgp-signature" Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Anshuman Aggarwal Cc: Mdadm List-Id: linux-raid.ids --Sig_/pXxQc7fhuBvi6RUVNC+qW_Q Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Tue, 16 Dec 2014 21:55:15 +0530 Anshuman Aggarwal wrote: > On 2 December 2014 at 17:26, Anshuman Aggarwal > wrote: > > It works! (Atleast on a sample 5 MB device with 5 x 1MB partitions :-) > > will find more space on my drives and do a larger test but don't see > > why it shouldn't work) > > Here are the following caveats (and questions): > > - Neil, like you pointed out, the power of 2 chunk size will probably > > need a code change (in the kernel or only in the userspace tool?) In the kernel too. > > - Any performance or other reasons why a terabyte size chunk may > > not be feasible? Not that I can think of. > > - Implications of safe_mode_delay > > - Would the metadata be updated on the block device be written to > > and the parity device as well? Probably. Hard to give a specific answer to vague question. > > - If the drive fails which is the same as the drive being written > > to, would that lack of metadata updates to the other devices affect > > reconstruction? Again, to give a precise answer, a detailed question is needed. Obviously any change would have to made in such a way to ensure that things which needed to work, did work. > > - Adding new devices (is it possible to move the parity to the disk > > being added? How does device addition work for RAID4 ...is it added as > > a zero-ed out device with parity disk remaining the same) RAID5 or RAID6 with ALGORITHM_PARITY_0 puts the parity on the early devices. Currently if you add a device to such an array ...... I'm not sure what it will do. It should be possible to make it just write zeros out. NeilBrown > > > > >=20 > Neil, sorry to try to bump this thread. Could you please look over the > questions and address the points on the remaining items that can make > it a working solution? Thanks --Sig_/pXxQc7fhuBvi6RUVNC+qW_Q Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIVAwUBVJCo4Tnsnt1WYoG5AQIrdQ//cUx9OA8Fgor+DTdmqkH446MK81iB75ug 4Eout3RinD06OjiWI+MneqDpdqCYY1eLaB2AG1LPfB8/kjvlaGdT0mVfr/2uTmjd KTk5MMwvhTd8Yw+lKfDwG3uboYmLjcWlxGtLHTMtIw0FmiWKOfxBJ8Erqh8w/Nz+ i05JA8fV5CgEANwkhMAw8Cq8b3DILeZ/dDab39rbv98/6EuOb747AY1/a01xQf2Q FFee5LMCwRTDGVaiX+cBTA1NabVFZy0k3+3BiETAQIu3HKRAmphzr7QL6xVWF53Q 0Id5FOj7HWr12XTHADolyN5CPKY77o+PQBBBKRRGxGcOEfPJR+fBbhzOucSjAPNY PiTDpZDlUAi0NvQGevvZZ3pD5riaDxKTBpcwv+NjMK4M5EiDiBG0uLYgh8dskt6l X6XjHpKynGZW2LlgAxHb1of144Vb/wnFCMa32Kibzjbhx4ce3YC3P29F9v+dDpDe lNYhC6GkbW757OJ5LlPAZaNoUjNplNc1zNvpH7xEzWZRCdbdR/VjoWyzpC1BNYlG wS4CkEmyhuMlhbzP/QAv3M6X5rcAGHoICQPb4dwIsaVEaJU1nq6d6BbASQ5QzGde a5KPvj1QNkplCfjgcjKFV2VR44rjWtLhOYqKpg5sXvFAYbBCtyEMXjez4BpNd9vw yksk6wzr0Ko= =UQcn -----END PGP SIGNATURE----- --Sig_/pXxQc7fhuBvi6RUVNC+qW_Q--