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82

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 ...


35

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 ...


32

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.


23

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? ...


22

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 ...


20

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 ...


16

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

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

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 ...


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 ...


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... ...


10

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 ...


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

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

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 ...


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 ...


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

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 ...


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

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

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.


8

Use RAID6. Read why here: http://www.zdnet.com/blog/storage/why-raid-6-stops-working-in-2019/805 on "Why RAID 6 stops working in 2019" by Robin Harris


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

That behavior (using a spare) should really be invisible to you; what it's saying there is that it's going to do some drive building trickery, and instead of sweeping the disks and building the parity channel up during the build (slow!), it's going to build the array on three devices and throw the last device in after the fact, to do the parity build in the ...


8

You're going to need a host with a SAS controller or an eraser appliance that supports SAS. As Chris S is pointing out, you can use SATA drives with SAS controllers, but not the other way around. As far as secure deletion, one pass with zeros will stop the amateurs, if you're worried about a TLA, make it one pass with random data, more if you're ...


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.


8

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 ...


8

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 it 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 from a ...


7

does a raid5 array always start in degraded mode at first ? Yes. At least, it always has for me. It makes sense; for any one of the disks to be able to fail, the disks must be synced. This will involve writing an equivalent of one whole disk's worth of data, which will take a while. Until this has been completed, the array is seen as ...


7

Having the databases on different spindles will most likely perform much faster if they are in use at the same time. If they experience busy periods that are offset from each other though a single RAID array will perform faster as a single database's reads will be spread over multiple drives (which it never will if it is on a single drive, of course). RAID5 ...



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