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Raid 5+0 https://3parug.com/viewtopic.php?f=18&t=2852 |
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Author: | Jim Mc [ Wed Apr 11, 2018 5:38 am ] |
Post subject: | Raid 5+0 |
Hi there, I'm trying to wrap my head around space consumption on a 7400. If I provision a thick volume of 5 TiB in size, it only results in a space consumption overhead of 27%. Which is about what I would expect for Raid 5, 3 Data + 1 Parity. But it should be double this quantity if it's including a mirror as well? Can anyone explain how come the mirror space doesn't appear to show? Here's how I worked it out: 5TiB thick provision in FC_r5 CPG FC space prior to provision: 28108.08 GiB FC space post provision: 21599.76 GiB Difference: 6508.32 6508.32 (actually used) / 5120 (provisioned) = 127% but I would expect this to be 252% due to raid 0 mirror? |
Author: | MammaGutt [ Wed Apr 11, 2018 6:41 am ] |
Post subject: | Re: Raid 5+0 |
RAID 0 is stripe, not mirror Not sure why you are expecting 2x the capacity usage |
Author: | Jim Mc [ Thu Apr 12, 2018 2:44 am ] |
Post subject: | Re: Raid 5+0 |
Not the first time I've gotten stripe and mirror mixed up. Now I'm even more confused though, because my understanding is raid 5 is a stripe anyway? Why does the documentation specify it as 5+0? |
Author: | MammaGutt [ Thu Apr 12, 2018 7:31 am ] |
Post subject: | Re: Raid 5+0 |
RAID 0 = stripe RAID 1 = mirror RAID 5 = single parity RAID 6 = dual parity A normal CPG could be Raid 5 (3+1) which means 3 data for each parity. As 3PAR is using wide-striping it is generally considered to be RAID 50 (or 5+0) when multiple 3+1 is used to generate a data set. Going a bit deeper, each disk in a 3PAR is divided into chunklets (1GB for Gen4 and Gen5 systems). Without the "+0" you wouldn't be able to have a volume (or CPG) larger than 3GB with RAID 5 (3+1). I would recommend reading pages 42-44 or something in the concepts guide https://support.hpe.com/hpsc/doc/public ... =c04204225 . |
Author: | Richard Siemers [ Thu Apr 12, 2018 9:49 pm ] |
Post subject: | Re: Raid 5+0 |
What documentation are you referring to with "5+0"? |
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