Date: Wed, 5 Jan 2011 22:55:01 +0100 From: Damien Fleuriot <ml@my.gd> To: Chris Forgeron <cforgeron@acsi.ca> Cc: "freebsd-stable@freebsd.org" <freebsd-stable@freebsd.org> Subject: Re: ZFS - moving from a zraid1 to zraid2 pool with 1.5tb disks Message-ID: <488AE93A-97B9-4F01-AD0A-0098E4B329C3@my.gd> In-Reply-To: <BEBC15BA440AB24484C067A3A9D38D7E0149F32D13E3@server7.acsi.ca> References: <4D1C6F90.3080206@my.gd> <ifsia5$5ub$2@dough.gmane.org> <4D21E679.80002@my.gd> <84882169-0461-480F-8B4C-58E794BCC8E6@my.gd> <BEBC15BA440AB24484C067A3A9D38D7E0149F32D13E3@server7.acsi.ca>
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Well actually... raidz2: - 7x 1.5 tb =3D 10.5tb - 2 parity drives raidz1: - 3x 1.5 tb =3D 4.5 tb - 4x 1.5 tb =3D 6 tb , total 10.5tb - 2 parity drives in split thus different raidz1 arrays So really, in both cases 2 different parity drives and same storage... --- Fleuriot Damien On 5 Jan 2011, at 16:55, Chris Forgeron <cforgeron@acsi.ca> wrote: > First off, raidz2 and raidz1 with copies=3D2 are not the same thing.=20 >=20 > raidz2 will give you two copies of parity instead of just one. It also gua= rantees that this parity is on different drives. You can sustain 2 drive fai= lures without data loss.=20 >=20 > raidz1 with copies=3D2 will give you two copies of all your files, but the= re is no guarantee that they are on different drives, and you can still only= sustain 1 drive failure. >=20 > You'll have better space efficiency with raidz2 if you're using 9 drives.=20= >=20 > If I were you, I'd use your 9 disks as one big raidz, or better yet, get 1= 0 disks, and make a stripe of 2 5 disk raidz's for the best performance.=20 >=20 > Save your SSD drive for the L2ARC (cache) or ZIL, you'll get better speed t= hat way instead of throwing it away on a boot drive.=20 >=20 > -- >=20 >=20 > -----Original Message----- > From: owner-freebsd-stable@freebsd.org [mailto:owner-freebsd-stable@freebs= d.org] On Behalf Of Damien Fleuriot > Sent: January-05-11 5:01 AM > To: Damien Fleuriot > Cc: freebsd-stable@freebsd.org > Subject: Re: ZFS - moving from a zraid1 to zraid2 pool with 1.5tb disks >=20 > Hi again List, >=20 > I'm not so sure about using raidz2 anymore, I'm concerned for the performa= nce. >=20 > Basically I have 9x 1.5T sata drives. >=20 > raidz2 and 2x raidz1 will provide the same capacity. >=20 > Are there any cons against using 2x raidz1 instead of 1x raidz2 ? >=20 > I plan on using a SSD drive for the OS, 40-64gb, with 15 for the system it= self and some spare. >=20 > Is it worth using the free space for cache ? ZIL ? both ? >=20 > @jean-yves : didn't you experience problems recently when using both ? >=20 > --- > Fleuriot Damien >=20 > On 3 Jan 2011, at 16:08, Damien Fleuriot <ml@my.gd> wrote: >=20 >>=20 >>=20 >> On 1/3/11 2:17 PM, Ivan Voras wrote: >>> On 12/30/10 12:40, Damien Fleuriot wrote: >>>=20 >>>> I am concerned that in the event a drive fails, I won't be able to=20 >>>> repair the disks in time before another actually fails. >>>=20 >>> An old trick to avoid that is to buy drives from different series or=20 >>> manufacturers (the theory is that identical drives tend to fail at=20 >>> the same time), but this may not be applicable if you have 5 drives=20 >>> in a volume :) Still, you can try playing with RAIDZ levels and probabil= ities. >>>=20 >>=20 >> That's sound advice, although one also hears that they should get=20 >> devices from the same vendor for maximum compatibility -.- >>=20 >>=20 >> Ah well, next time ;) >>=20 >>=20 >> A piece of advice I shall heed though is using 1% less capacity than=20 >> what the disks really provide, in case one day I have to swap a drive=20 >> and its replacement is a few kbytes smaller (thus preventing a rebuild). > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org"
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