From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Evans Subject: Re: What RAID type and why? Date: Sun, 7 Mar 2010 02:09:33 -0800 Message-ID: <4877c76c1003070209vd40c8b9x11edde7d793ad378@mail.gmail.com> References: <5bdc1c8b1003061402n1281b64es9fa597b8bc714bd5@mail.gmail.com> <87f94c371003061433x404a8c2fgcb61f817af6ecb1@mail.gmail.com> <9089562724D84B3C858E337F202FF550@m5> <20100307132113.7e2c95b6@notabene.brown> <20100307080638.GA30126@light.rap.dk> <20100307082256.GB30126@light.rap.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20100307082256.GB30126@light.rap.dk> Sender: linux-raid-owner@vger.kernel.org To: Keld Simonsen Cc: Guy Watkins , Neil Brown , Greg Freemyer , Mark Knecht , Linux-RAID List-Id: linux-raid.ids On Sun, Mar 7, 2010 at 12:22 AM, Keld Simonsen wrote: > On Sun, Mar 07, 2010 at 03:10:18AM -0500, Guy Watkins wrote: >> } -----Original Message----- >> } From: Keld Simonsen [mailto:keld@keldix.com] >> } 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" wrote: >> } > >> } > > } >> } > > } At a minimum I would build a 3-disk raid 6. =A0raid 6 does a= lot of >> } i/o >> } > > } which may be a problem. >> } > > >> } > > If he only needs 3 drives I would recommend RAID1. =A0Can stil= l 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 th= e 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? =A0I did not think it w= orked that >> way. =A0I thought RAID10 maintained 2 copies, not 3. =A0But I have n= ever used >> RAID10. > > If you ask mdadm to do it, yes. Example: > > mdadm --create /dev/md3 --chunk=3D256 -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@vger.kernel.org > More majordomo info at =A0http://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" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html