If I had 4 hard drive in RAID5 and 2 failed, did I lose everything?
That is the typical type of question a person would use to justify not using RAID5 when they had a choice to use it. Chances of all your hard drives being taken out in a RAID 5 array when the tornado lifts your mobile home off the ground and smashes up your computer would be about the same result. Common, lets be realistic; Hard drives don't always completely fail nor all at the same time and most of the time give you warning that they are failing while operating in a reduced performance. Chances are slim at best that you loose more than one drive at once. If you don't trust me, use RAID 6 or some other RAID that supports multiple redundant parity drives.
More information on failures with Hard Disc Drives: http://www.overclockers.com/tips1035/index06.asp
About Data recovery.. I one day was trying to upgrade another computer's measly 20gb hard drive with a 200Gb hard drive. I was using an application called Paragon Partition Manager, copying the hard drive, when my power supply blew out. What are the chances of that! Seemed that the Paragon software modifies the boot sectors on all hard drives while it is in use, and the power interruption took out my software Spanned array, both source and destination hard drive and my C: drive. No problems with recovering my C: drive as I re-installed windows XP with the repair option (And re-install most my apps) BUT, Alas the spanned array was non-recoverable. Windows XP kept running out of memory when trying to re-attach the devices.
I wasn't about to accept this. Family pictures and the lot of personal stuff over 10 years worth LOST!
After 2 weeks of research and trying different software, I came to this conclusion, 100% data recovery from the array.
1: Re-create the array without a format
2: Run a deep scan using Runtime Software's Getdataback NTFS.
I simply connected another computer on the network and copied all the files over while in Windows XP. Took about 4 hours to scan 250Gb in four hard drives spanned and about a day to copy it.
So, sometimes you can recover data with damaged arrays.
I also found File scavenger partially usefull, as it had an option to select several physical hard drives in Raid 0, 1, 5, or jbod emulation to recover data, but it was able to recover only 75% of my data. 25% of the files were cross-linked with the contents of other files and was not a viable solution, but the option was a creative one which the other competing products did not come with.
I would mention the other software here as well, but since they didn't work completely, or at all, their names are not worth mentioning.
I since built a RAID 5 array using six 400GB drives and keeping a spare 400GB in my computer powered up and not used, so when I have another one fail, I don't loose anything and rebuilding can be done without swapping or fussing. I also since had one of those 400Gb drives fail, and I found that with software RAID 5, I was unable to use the device until it was completely rebuilt as it was not properly calculating parity until the spare drive was rebuilt in the array.
If anyone is into Hardware RAID, 3ware
sells some expensive and impressive RAID cards in different form factors, (PCI-X, PCI-E) in 4, 8, 12, and more SATA ports. For the price, I am certain that performance would be impressive. But if you have a 3Ghz P4 or a 2Ghz AMD machine, you would be looking about 8Mb/s write speed with software RAID 5. Not that bad. I however have had poor customer service and poor results using Highpoint cards, but found them to be more flexible on features. I would generally suggest a buyer beware for Highpoint. Promise cards however have never given me troubles and have always been true to specifications even when they were limited in available features.
Another interesting thing I do with my RAID cards, is do a multi-nested RAID setup. I can Stripe pairs of hard drives and then Software RAID 5 them together, or Jbod (Span) pairs up for capacity and then RAID 5 them. This way I can combine drives of dissimilar capacities using Jbod in order to make up arrays with the same sizes and then Raid 5 them together. If one or more of the drives fail in a Jbod array, I simply take out all the drives in that array and replace those drives with one of equal size or rebuild the jbod with another set of dissimilar hard drives which equal or exceed the minimum hard drive capacity for that set of devices in the RAID 5 array.
Most RAID Cards also do not offer your operating system to monitor SMART status (Self-Monitoring, Analysis and Reporting Technology
) of your physical discs as well, so when your SMART reports issues which could identify possible problems in the near future with your hard drive, you are simply not informed about it until it actually fatally fails. (SMART monitor software: http://www.hdsentinel.com/
) For this reason, software RAID could be a feasible option. I hear however that the newer "More expensive" Raid cards come with their own monitoring software, but to what type of available information they pass onto the user I don't know.
If your machine has plenty of room for hard drives and you got a hefty power supply, playing with arrays can be fun.