How can we recover data from Hard Drives were on RAID 10 without controller?
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@scottalanmiller said in How can we recover data from Hard Drives were on RAID 10 without controller?:
@Pete-S said in How can we recover data from Hard Drives were on RAID 10 without controller?:
So it's a pure sequential read on all drives in the array and a sequential write on the drive being rebuilt. Starting from the outside of the disk platters and moving in.
Can't be sequential because it has to skip over the parity, it's nearly sequential, but not quite. And if there is any production traffic, all sequential is gone.
It makes sense to believe that, since RAID-6 only needs data from N-2 drives to recreate what's missing.
However it reads from all drives because it's much faster to calculate the missing data when you have N-1. It's a math thing. If you check the source code for the md driver in the kernel you'll see it mentioned several times.The other factor is that it is head movements that destroys the sequential performance. The drive that had the data you could calculate, instead of reading, is just spinning. It doesn't do anything else and can't do anything by itself. So you won't lose anything even if you'd skip one stripe segment on one drive. It wouldn't lower the performance of the rebuild except increasing the amount of data that need to be calculated.
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@Pete-S said in How can we recover data from Hard Drives were on RAID 10 without controller?:
However it reads from all drives because it's much faster to calculate the missing data when you have N-1. It's a math thing. If you check the source code for the md driver in the kernel you'll see it mentioned several times.
Oh right, because it's a different calc each time. One time it's p, one time it's q, one time it's 1 and so forth.
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@scottalanmiller said in How can we recover data from Hard Drives were on RAID 10 without controller?:
@Pete-S said in How can we recover data from Hard Drives were on RAID 10 without controller?:
However it reads from all drives because it's much faster to calculate the missing data when you have N-1. It's a math thing. If you check the source code for the md driver in the kernel you'll see it mentioned several times.
Oh right, because it's a different calc each time. One time it's p, one time it's q, one time it's 1 and so forth.
Yes, and it's the double parity (Q) that is very costly in CPU to calculate. The actual math for the double parity is advanced stuff, way beyond me. But if you have one failed drive you only have to do the double parity calculation every N stripes to be able to rebuild the drive. If you have two failed drives you have to do it every stripe. That's why it's less CPU/energy/heat consuming to just read all the drives when rebuilding.
In general I think that people who have problems rebuilding RAID-6 arrays have two problems.
- They just pop in the replacement drive and wait. Not knowing that they need to adjust the rebuild priority unless they want to wait forever.
- They made a design fail, ie wrong type / size of array for the job in question. And now they're paying the price.
RAID-6 arrays also have a tendency to big large arrays with large drives, exacerbating the problem.
And I think people are over-consolidating in their excitement to consolidate everything. Basically ending up with all the eggs in one basket.
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@Pete-S said in How can we recover data from Hard Drives were on RAID 10 without controller?:
Yes, and it's the double parity (Q) that is very costly in CPU to calculate. The actual math for the double parity is advanced stuff, way beyond me. But if you have one failed drive you only have to do the double parity calculation every N stripes to be able to rebuild the drive.
Yeah, I was trying to allude to that in what I had said. Only when replacing the P, I think, it needs that.
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@Pete-S said in How can we recover data from Hard Drives were on RAID 10 without controller?:
They just pop in the replacement drive and wait. Not knowing that they need to adjust the rebuild priority unless they want to wait forever.
Or.... they should have their rebuild priorities adjusted as a standard based on the assumed workload needs and only adjust later if something special has happened.
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@Pete-S said in How can we recover data from Hard Drives were on RAID 10 without controller?:
RAID-6 arrays also have a tendency to big large arrays with large drives, exacerbating the problem.
This is a complex logic. It's something like...
Large arrays tend to use spinners. Spinners tend to use RAID 6 or 10. Large arrays tend to be costly for RAID 10. etc.
But a huge selling point for RAID 10 is that recovery time is flat. Keep adding drives, the recovery time doesn't change. RAID 6, every additional drive can add a bit of time.
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@Pete-S said in How can we recover data from Hard Drives were on RAID 10 without controller?:
And I think people are over-consolidating in their excitement to consolidate everything. Basically ending up with all the eggs in one basket.
We see this a lot. There is certainly a desire for "one pool of storage" and it's so easy now that 10TB drives are so cheap. Heck, I bought one for my kids' video games. 10TB Helium 6Gb/s SATA drive with 256MB cache on my children's video game machine!
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Have you checked the SMART values to make sure the drives are degraded and bad? If the drives are good a simple chkdsk may resolve your issues
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I recently arranged two 8TB hard drives to clone the drives. Already done with cloning from Disk 2 and Disk 4.
Now reconstructing RAID 0 and trying to recover the data. I tried a couple of software which were saying free and after reconstructing RAID, to recover data it started saying Evaluation.
Is there any open source or completely free software for this requirement?
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@openit said in How can we recover data from Hard Drives were on RAID 10 without controller?:
I recently arranged two 8TB hard drives to clone the drives. Already done with cloning from Disk 2 and Disk 4.
Now reconstructing RAID 0 and trying to recover the data. I tried a couple of software which were saying free and after reconstructing RAID, to recover data it started saying Evaluation.
Is there any open source or completely free software for this requirement?
None that I know of.
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@openit said in How can we recover data from Hard Drives were on RAID 10 without controller?:
I recently arranged two 8TB hard drives to clone the drives. Already done with cloning from Disk 2 and Disk 4.
Now reconstructing RAID 0 and trying to recover the data. I tried a couple of software which were saying free and after reconstructing RAID, to recover data it started saying Evaluation.
Is there any open source or completely free software for this requirement?
NO. If your data is important, pay for the software. otherwise, why bother.
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Okay, got it, name some paid software, for RAID data recovery, known to be working or from your experience.
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@openit www.runtime.org
GetDataBack for NTFS with RAID Reconstructor.
We've had excellent success with their product. -
@openit said in How can we recover data from Hard Drives were on RAID 10 without controller?:
Okay, got it, name some paid software, for RAID data recovery, known to be working or from your experience.
@CCWTech does this every day.
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@openit said in How can we recover data from Hard Drives were on RAID 10 without controller?:
Okay, got it, name some paid software, for RAID data recovery, known to be working or from your experience.
Unless you are starting a data recovery firm, it's likely going to be way cheaper to have a service do this rather than to invest in recovery firm tools for one time use.
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@PhlipElder said in How can we recover data from Hard Drives were on RAID 10 without controller?:
@openit www.runtime.org
GetDataBack for NTFS with RAID Reconstructor.
We've had excellent success with their product.Yeah I've had good results with GetDataBack, it with harddrives not tried RAID bit will be soon.
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You don't need a RAID card, in fact don't use one. There is a chance it will overwrite your data. Clone the drives, ONLY work on clones, never on patient drives.
UFS Explorer Professional
ReclaimMe Pro -
@CCWTech said in How can we recover data from Hard Drives were on RAID 10 without controller?:
You don't need a RAID card, in fact don't use one. There is a chance it will overwrite your data. Clone the drives, ONLY work on clones, never on patient drives.
UFS Explorer Professional
ReclaimMe ProWhat would you recommend for the cloning side of things?
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@hobbit666 said in How can we recover data from Hard Drives were on RAID 10 without controller?:
@CCWTech said in How can we recover data from Hard Drives were on RAID 10 without controller?:
You don't need a RAID card, in fact don't use one. There is a chance it will overwrite your data. Clone the drives, ONLY work on clones, never on patient drives.
UFS Explorer Professional
ReclaimMe ProWhat would you recommend for the cloning side of things?
If the drives are healthy, something like ddrescue does a good job. Cloning the entire drive (even empty sectors) is best.
If the drives are NOT healthy, you need professional data recovery equipment. (Ace Labs PC-3000 or at minimum a Deepspar DDI4). If you have a drive with a physical problem and you try to image it w/o professional data recovery gear, you have a good chance of never seeing the data again.
