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83

Ok - something was bugging me about your issue, so I fired up a VM to dive into the behavior that should be expected. I'll get to what was bugging me in a minute; first let me say this: Back up these drives before attempting anything!! You may have already done damage beyond what the resync did; can you clarify what you meant when you said: Per ...


36

Your options are: Restoring from backups. You do have backups, don't you? RAID is not a backup. Professional data recovery It's possible, though very expensive and not guaranteed, that a professional recovery service will be able to recover your data. Accepting your data loss and learning from the experience. As noted in the comments, large SATA ...


35

You have a double disk failure. This means your data is gone, and you will have to restore from a backup. This is why we aren't supposed to use raid 5 on large disks. You want to set up your raid so you always have the ability to withstand two disk failures, especially with large slow disks.


25

You have disadvantages and advantages with each approach; it depends on why you're using RAID. Most people use it for availability. They don't want a drive to die and end up having to take their system or server down. In that, you don't use RAID 5. I learned it the hard way and hammer this point home with every RAID-related question I get into on SF. Why? ...


23

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 array this is no problem since the missed read ...


21

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 ...


17

Why would you ask the internet about this? There's so much WTF here, that I don't understand where to start!! This question shows a fundamental lack of understanding of hardware, RAID arrays, storage, monitoring, and general IT best-practices. I read this question and can't help but think: Who is actually responsible for this server hardware? Where is ...


17

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 is <0.5% chance of failure, but could be ...


15

Your system I assume is still up, so the best thing to do is make an immediate backup, dump the disks/array, rebuild, and restore from the backup. Bad blocks don't always mean your backups are also bad. If you haven't experienced any performance problems or damaged files, then your backups should still be complete enough to finish a restore. To test, take ...


15

They both are. It depends on the application using the array, the number of disks in the raid group and the IO requirements of the applications sitting on them. For example a file server probably doesn't need RAID 10 as the bulk of the data is just sitting there with a few users opening and closing files through out the day. An OLTP database may need a ...


14

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 a sector-level copy with a lowlevel disk cloning ...


13

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... ...


13

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 can get a compatible part covered by ...


12

How appropriate, that this should come on the heels of "Backup Appreciation Week" (or whatever it's called). The problem with trying to do anything yourself is that you're just increasing the amount of degradation on the drives whenever you're running them. Decide now if you're going to send it to the pros, and if so, just do it. Presumably if this data ...


12

You really kinda need the original mdadm.conf file. But, as you don't have it, you'll have to recreate it. First, before doing anything, read up on mdadm via its manual page. Why chance loosing your data to a situation or command that you didn't have a grasp of? That being said, this advice is at your own risk. You can easily loose all your data with the ...


11

Use RAID6. Read "Why RAID 6 stops working in 2019" by Robin Harris on ZDNet.


10

Using RAID5 with this configuration, you introduce additional risk to your RAID. With the storage density introduced with modern disks, the likelihood of encountering a bad block on multiple disks is higher. If using 1TB+ disks, it's recommended to use a RAID6 as opposed to RAID5, as it has an additional parity disk. If you want greater speed as well as ...


10

Before you try anything, I would plug the drives into a non-RAID-controller and dumping them byte by byte (e.g. via dd) onto some other storage. Then you can do whatever you want - you have a backup.


10

Drives can be marked as failed in an array for many reasons. Maybe there's a few defective sectors. Maybe the drive heads are failing. Maybe cosmic rays hit your drive at the right angle and time to fail a scan. Maybe their firmware has a bug that breaks under . Some of these are reparable failures, some aren't. The thing is, it's really hard to predict ...


10

You are laboring under a serious misconception. RAID is not a form of backup. If you accidentally delete a file, or a software bug commands the system to overwrite files, the RAID system will cheerfully propagate the data loss to all drives. If something goes wrong in the RAID controller or the RAID headers get corrupt, you may be unable to get the RAID ...


10

With RAID 5 you can only lose 1 disk and have your data remain available. You have lost 3 so you will need to rebuild the RAID and then restore the data from backup. We have a canonical Q&A about RAID levels that may help your understanding.


9

You'd be left with only half the capacity, so if the file system was more than half full already, it would be impossible. Even if there is sufficiently free space, the operation involves resizing the file system, which requires intimate knowledge of the file system. Moreover applying ordinary resizing tools to a degraded RAID5 before converting it to RAID1 ...


9

You've had a double drive failure, with one of the drives being dead for six months. With RAID5, this is irrecoverable. Replace the failed hardware and restore from backup. Going forward, consider RAID6 with large drives like this and make sure you have monitoring in place to catch device failures so you can respond to them ASAP.


9

This is a bit crazy... A Smart Array P600 PCI-X RAID controller (circa 2005)?!? 25 disks? RAID 5? Is this an HP MSA70 enclosure? Is probably not the HP D2700? "Ready for Rebuild" is about the worst array status message you can receive on an HP ProLiant system. This indicates that the logicaldrive can't finish its rebuild because there's trouble reading ...


9

The reason that article exists is to draw attention to Unrecoverable Bit Error Rates on HDDs. Specifically, your cheap 'home PC' disks. They typically have a factory spec of 1 / 10^14. This is about 12.5TB of data, which if you are doing a RAID-5 with 2TB disks ... you hit quite quickly. This means you should either: use smaller RAID groups, and accept ...


9

Regardless of how many drives are in use, a RAID 5 array only allows for recovery in the event that just one disk at a time fails. What 3molo says is a fair point but even so, not quite correct I think - if two disks in a RAID5 array fail at the exact same time then a hot spare won't help, because a hot spare replaces one of the failed disks and rebuilds ...


9

There's lots of similar questions/arguments on this site regarding R10 vs. R5/R6 but they boil down to "exposure during rebuild". The argument for R10 over R5 is strongest when dealing with the larger, slower disks some buy because their GB/$£€ is better (i.e. 2/3TB 7.2k SATAs) as arrays of these disks can take literally days to rebuild following a disk ...


9

These raids are all relative to each-other assuming the same disks and controller in the array. Raid5: Good read speed, rotten write speed, can survive any double disk failure if the failures occur over enough time for the raid to rebuild between failures. (ie disk fails, raid rebuilds, disk fails, you're okay). If you have simultaneous double disk ...


8

You had me a R5 - don't. The reason is that in the event of a disk failure you have zero protection until you've replaced the disk and the array has rebuilt. For large cheapo SATA disks this rebuilt process can take DAYS - meanwhile you are at the mercy of a second disk failing - at which point it's game over. Also this type of disk is rarely happy to ...


8

Yes, in this case, you would pull the bad drive and insert the new drive. HP Smart Array controllers initiate the rebuild process automatically. This can be done hot, while the system is running. A description of the HP Smart Array RAID controller technology is available here.



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