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mdraid 5 speed, 3 disk vs 4 disk vs more?

 
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jamespotter


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MessagePosté le: Sam 26 Mai - 11:42 (2018)    Sujet du message: mdraid 5 speed, 3 disk vs 4 disk vs more? Répondre en citant

Hello,


Not another mdraid 5 speed problem thread??? Actually, no, I just wanted to post an observation which somewhat baffles me. For the past (more than) a decade I've been running 4-disk RAID5's so that I could have a 25% overhead ratio. I was getting miserable write rates (a less than the speed of one disk), and if lucky read rates got about the speed of two raw disks. My first RAID was PATA, and the second RAID was SATA. The PATA raid worked beautifully for many years with absolutely no disk failures. A few minor disk kicks but was easily recoverable. On the other hand, I had all sorts of problems with my first SATA RAID. Lost disks left and right. It got to the point I stopped putting fresh disks into the array and ran degraded. ... up until a few days ago, another disk kicked the bucket. 4 disk RAID with 2 good members? Byebye data 
Fortunately it wasn't that bad. I knew I was running a ticking timebomb, so I frequently backed up to a new RAID on another machine, this time a new, bigger 3-disk RAID5 on a slow machine, separate so that it counts as an offline backup. When that last straw disk died that took the old RAID down and out, it took a few hours but finally got the new 3-disk RAID5 (with its 33% space overhead) up and running booting once more. I only had to do one restore as I just so happened to backup the disks just before it failed, so I have a very fresh data set minus one volume on the LVM. 



Please help


I didn't find the right solution from the internet.


References: 
https://forums.gentoo.org/viewtopic-p-8100900.html?sid=77baefb4642e253f2176948ac5c6e96b
Digital production service



Thanks


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MessagePosté le: Sam 26 Mai - 11:42 (2018)    Sujet du message: Publicité

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