Questions about MD 2-drive RAID-10
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From: Nathan Eisenberg <hidden>
Date: 2012-01-12 23:27:06
Hi there, It's my first post here! For some background, I'm a sysadmin at a datacenter provider. I have a large number of MD devices under my control, and a fair amount of experience using MD and the majority of its RAID drivers. Just so I've said it, I did quite a lot of searching before deciding to post, in the hopes that I could find my answer documented somewhere. If I've missed a good article where my question was clearly answered, then I do apologize (and feel free to mock me for it)! Until a few hours ago, I was under the impression that a RAID-10 required at least four disks, in pairs that form the underpinning mirrors for the stripe. A few days ago, a customer of mine requested a two drive RAID-10, and was surprised by my insistence that it was impossible. Imagine my shock when I stumbled across http://neil.brown.name/blog/20040827225440. http://en.wikipedia.org/wiki/Non-standard_RAID_levels#Linux_MD_RAID_10 This article talks about MD's RAID-10 driver's support for a 2-disk RAID-10, in both 'near' and 'far' modes. It also mentions the potential performance advantages (over a RAID-1) of using the RAID10 driver in the 'far' configuration on a 2-disk array, but it doesn't say much about the 'near' mode. My question is this: what differences, if any, are there between building a RAID-1 with two disks, and building a RAID-10 with two disks in the 'near' configuration? Does this result in the OS 'striping' its reads across the mirrored disks, improving read (but presumably not write) access? Do I correctly interpret the article's suggestion that the 'far' configuration will result in increased performance for both reads and writes (again, over a RAID-1), or am I crazy? Thank you for your time! Nathan