Re: What's the typical RAID10 setup?
From: Mathias Burén <hidden>
Date: 2011-01-31 21:24:13
2011/1/31 Roberto Spadim [off-list ref]:
no matter what raid1 or raid10 system we use raid1 is mirror! let´s think that raid0 = more than one disk (not a single disk)... if a hard disk inside a mirror (raid1) fail (it can be a raid0 or a single disk) the mirror is failed for example: there´s no 25% survival for 2 mirrors with 4 disks! probability, here, is mirror based, not disk based! it´s not a question about linux implementation is a question for generic raid1 (mirror) system (1 failed 2 mirrors = 1 mirror failed but 1 mirror working) you only can have 25% 'survival' if you can use 4 disks, or multiples of 4, for raid1 if your raid0 is broken you don´t have a raid0! you have a broken raid = broken mirror (for raid1)! should i write it again? for raid10 (raid1+0) with 4 disks you can only lost 1 disk! 1 disk lost = 1 raid0 lost = 1 mirror lost! should i write it again? 2011/1/31 Keld Jørn Simonsen [off-list ref]:quoted
On Mon, Jan 31, 2011 at 02:17:37PM -0600, Stan Hoeppner wrote:quoted
Keld Jørn Simonsen put forth on 1/31/2011 1:28 PM:quoted
Top-posting... How is the raid0+1 problem of only 33 % survival for 2 disk with RAID10? I know for RAID10,F2 the implementation in Linux MD is bad. It is only 33 % survival, while it with a probably minor fix could be 66%. But how with RAID10,n2 and RAID10,o2?I don't care what Neil or anyone says, these "layouts" are _NOT_ RAID 10. If you want to discuss RAID 10, please leave these non-standard Frankenstein "layouts" out of the discussion. Including them only muddies things unnecessarily.Please keep terminology clean, and non-ambigeous. Please refer to the old term RAID10 as RAID1+0, which is also the original and more precise term for that concept of multilevel RAID. RAID10 on this list refers to the RAID10 modules of the Linux kernel. I can concurr that this may be a somewhat misleading term, as it is easily confused with the popular understanding of RAID10, meaning RAID1+0. And I see Linux RAID10 as a family of RAID1 layouts. Indeed RAID10,n2 is almost the same as normal RAID1, and RAID10,o2 is an implementation of a specific layout of the RAID1 standard. RAID10,f2 could easily also be seen as a specific RAID1 layout. But that is the naming of terms that we have to deal with on this Linux kernel list for the RAID modules. 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 http://vger.kernel.org/majordomo-info.html-- Roberto Spadim Spadim Technology / SPAEmpresarial -- 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 http://vger.kernel.org/majordomo-info.html
In a 4 disk RAID1+0 (where you have 2 HDDs in RAID1 (a) and 2 other HDDs in RAID1 (b), then put them together in a RAID0) you can lose a maximum of 2 HDDs, without any data loss. Sure, the "mirror" is "broken", but your data is intact. So, you can actually rip out 2 HDDs and still have your data, providing you pull the "right" drives. A single disk can be described as RAID0 (as it's not redundant). // Mathias -- 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 http://vger.kernel.org/majordomo-info.html