On Sun, Mar 7, 2010 at 12:22 AM, Keld Simonsen <keld@xxxxxxxxxx> wrote: > On Sun, Mar 07, 2010 at 03:10:18AM -0500, Guy Watkins wrote: >> } -----Original Message----- >> } From: Keld Simonsen [mailto:keld@xxxxxxxxxx] >> } Sent: Sunday, March 07, 2010 3:07 AM >> } To: Neil Brown >> } Cc: Guy Watkins; 'Greg Freemyer'; 'Mark Knecht'; 'Linux-RAID' >> } Subject: Re: What RAID type and why? >> } >> } On Sun, Mar 07, 2010 at 01:21:13PM +1100, Neil Brown wrote: >> } > On Sat, 06 Mar 2010 18:17:44 -0500 >> } > "Guy Watkins" <linux-raid@xxxxxxxxxxxxxxxx> wrote: >> } > >> } > > } >> } > > } At a minimum I would build a 3-disk raid 6. raid 6 does a lot of >> } i/o >> } > > } which may be a problem. >> } > > >> } > > If he only needs 3 drives I would recommend RAID1. Can still loose 2 >> } drives >> } > > and you don't have the RAID6 I/O overhead. >> } > > >> } > >> } > and as md/raid6 requires at least 4 drives, RAID1 is not just the best >> } > solution to survive two failures on a 3-device array, it is the only >> } solution. >> } >> } Raid10 can also do it. >> } >> } raid1 is in many ways obsolete and you should rather use raid10, >> } which in my eyeys is just another way of doing the same conceptual thing >> } as raid1. >> } >> } Best regards >> } keld >> >> Are you sure RAID10 can loose 2 of 3 drives? I did not think it worked that >> way. I thought RAID10 maintained 2 copies, not 3. But I have never used >> RAID10. > > If you ask mdadm to do it, yes. Example: > > mdadm --create /dev/md3 --chunk=256 -R -l 10 -n 3 -p f3 /dev/sd[abc]1 > > the "-p f3" is the one that asks to have 3 copies. > > best regards > keld > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Yes, that way would work, except in that case it would use more complicated methods to split up the stripes among the drives. Since you're application seems to be read heavy, I agree with using 'far' for the stripe method. However the dis-advantage of mdadm raid10 has been two-fold compared to raid1 (until kernel 2.6.33+). 1) Fixed in 2.6.33: Striped storage did not previously support write-barriers (required for atomic write mechanisms/journals). 2) Still unsupported? : Reshape of raid10 arrays. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
