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12

Please use RAID 1+0 with your controller and drive setup. If you need more capacity, a nested RAID level like RAID 50/60 could work. You can get away with RAID 5 on a small number of enterprise SAS disks (8 drives or fewer) because the rebuild times aren't bad. However, 24 drives is a terrible mistake. (Oh, and disable the individual disk caching feature... ...


10

The key to the answer to your question is read-ahead. Once upon a time, I also happened to have that issue. IOW, for optimal sequential read performance all disks should be permanently involved into Input. When you use dd w/o directio (see man dd), write operation is not being performed immediately, but goes through OS cache, so it has more chances to ...


8

poige is exactly right about the write cache, but here are more details. dd with zeros and using write cache is not the right way to benchmark (unless you want to test the write cache of course, which is probably only useful for a file system, to see how much it syncs metadata, creates new files, etc.) (and likely dd is always the wrong type of benchmark, ...


6

Do NOT use a single RAID 5 array across 24 1TB disks! I don't much care what you prefer to limit the answers to, it's a bad idea and you should look at other options. The odds of a disk failing go up with each disk. So does the time it takes to rebuild. When a drive fails, and you replace it, it will use as much IO across all the disks as possible to ...


4

Converting a live boot/root disk to RAID is a lot of magic and usually it is not worth the effort. You are better off with moving to the new disk first. Start it up as a degraded raid-1, copy the contents (not clone). Then work on booting the system from it. Depending on the OS used that can be a lot of fun too. After you are able to boot from the new ...


1

The only difference I see is this line: #DEVICE partitions This is commented out in the generated config file but not yours. I'd just uncomment that and commit the changes. Warnings like that tend to be a "head's up" thing rather than an actual problem if the configurations line up.


1

Reading your configuration, I see: 8 disks total... Disks 1,2,3,4 are in a RAID 1+0 array. Disks 5,6 are in a RAID 0 stripe. Disks 7,8 are in a RAID 0 stripe. I'm not going to ask why you have two RAID 0 arrays. Surprisingly, they're healthy! It looks like disk 2 was replaced. It's paired with disk 4. You could likely have READ errors on disk 4 that ...



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