Designing the reliability of a disk array: Find the URE Rate of your drive (manufacturers don’t like to talk about their drives failing, so you might have to dig to find this. It should be 1/10^X where X is around 12-18 commonly). Decide what is an acceptable risk rate for your storage needs†. Typically this … Read more
RAID-5 is a fault-tolerance solution, not a data-integrity solution. Remember that RAID stands for Redundant Array of Inexpensive Disks. Disks are the atomic unit of redundancy — RAID doesn’t really care about data. You buy solutions that employ filesystems like WAFL or ZFS to address data redundancy and integrity. The RAID controller (hardware or software) … Read more
I think you’ve got it right. Make sure you understand and heed the warnings regarding growing RAID 5 in man 8 mdadm. Personally if I were growing an LVM volume, I would not be growing an existing RAID array to do it. I’d create another RAID array, create a new physvol from it, and add … Read more
The terminology you are looking for is a “RAID level migration”. According to this, it’s possible. I haven’t done it, but the procedure looks like you should add the new drive as a hotspare to the existing array, then use mdadm to update the raid level and the number of raid devices.. You’ll need a … Read more
To answer your questions, Can it be restored? First thing’s first – STOP, sit back and just think a little. Yes, algorithm, chunk size and disk order is vital to getting whatever filesystem that was present, to properly re-assemble. But since you’ve overwritten the superblocks, you’re now left with trial and error. Second, is there … Read more
Besides whatever metadata the RAID controller uses, are there any differences between these two arrays (in terms of data layout, performance, reliability)? Yes. RAID5 uses a single, rotating parity while RAID6 uses two. You may be visualizing dedicated parity disks, but they’re in fact rotating. RAID5 should be rather straight-forward: With RAID6, imagine the last … Read more
The system is running very slowly because it has to reconstruct the missing data which involves additional CPU and I/O. If you have a missing disk in a RAID-5 configuration you have no recovery strategy. If another disk goes down you will lose your data. Run, don’t walk, to the nearest vendor from which you … Read more
I’ve wrestled with this question for a while. There are a number of factors determining how many disks should go into a RAID5 array. I don’t know the HP 2012i, so here is my generic advice for RAID5: Non-recoverable read error rate: When a non-recoverable read error occurs, that read fails. For a healthy RAID5 … Read more
Your reasoning is correct, though you’re missing the scale of the problem. Enterprise SSDs are being made with higher endurance MLC cells, and can tolerate very high write-rates. SLC still blows high-endurance MLC out of the water, but in most cases the lifetime write-endurance of HE-MLC exceed the expected operational lifetime of a SSD. These … Read more
After you accepted a bad answer, I am really sorry for my heretic opinion (which saved such arrays multiple times already). Your second failed disk has probably a minor problem, maybe a block failure. This is the cause, why the bad sync tool of your bad raid5 firmware crashed on it. You could easily make … Read more