What is "RAID" and why is "RAID 0" such a bad, bad idea?

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> If one drive has, say, a 1 in 1,000 chance of failure, then two drives have a 1.9989(9) in 1,000 chance.

As a maths geek I feel obliged to make an unnecessary, pointless, and anal correction: If one drive has a 1 in 1,000 chance of failure (in some time period), then two drives have a 1.9989(9) in 1,000 chance of either failing (where brackets denote recursion).

(Yes, I know you know that and were just approximating it as 2, Leo, but it's good not to get your readers into the habit of assuming probabilities are additive: otherwise they end up thinking things like "So if each drive has a 75% chance of having failed by the end of 20 years, then two drives have a 150% chance of one of them having done so" (the actual figure would be 93.75%).)

Simon, I know that the combined probability isn't 2, but how did you get 1.9989(9) in 1,000? I get 1.999.

P(no failure in single disk) = 0.999
P(no failure in either disk) = 0.999 * 0.999 = 0.998001
P(failure in either disk) = 1 - 0.998001 = 0.001999 (or 1.999 in 1,000)

Did I forget something? I wouldn't be shocked.

I've heard that RAID 5 doesn't give you the speed of 0 or the security of 1, just the illusion of both.

Just do RAID 10. All the redundancy of RAID 1 with all the speed of RAID 0.

Of course, redundancy or not, there's no substitute for backing up your data. Having a single drive in a RAID 0 array go kablooey is no different than having the one drive in a single drive system go kablooey. You're still going to have to restore from a backup.

RAID - SPLIT PERSONALITY- NEVER WORKS

O.K.,
So I'm a victim of Raid 0. My old MB had a built-in controller and I foolishly used it. Sure enough one of my WD drives failed. (I think it's in the PCB and not the platters, but anyway)
My question is: Can the data from one drive be recovered professionally to be synced with the remaining drive, or do both drives need to be "sent in"? Of course that's double the GB's for recovery cost.
RAID 0 - never again!

I'd go a bit farther and suggest that RAID 1 or 5 are also bad ideas for the ordinary home user. One of the more common problems I've seen in servicing Windows computers is file system corruption that is easily resolved by running scandisk from the Recovery Console. But if the boot volume is on a RAID, the user will need to load drivers in order to access it from the Recovery Console. It can become a mess. On occassion when I didn't have access to the correct drivers or the user had no floppy drive, I've had to break the RAID, fix the file system and then rebuild the RAID. Not for the faint of heart and NOT for the ordinary user.

RAID is also sometimes seen as a substitute for backup and it shouldn't be.

As far as the speed or storage space benefits, I think they are minor for most users.

I'll throw out a speculation at improving performance and a possible backup scheme/arrangement: If you buy into a computer with multiple drives, use the fastest one(DMA and spindle speed and latency) for either or the system and cache(swap file); or, if you have enough fast disks, perhaps have the larger(GB) of the two(or more) be used to install the OS and applications. Use the other one(s) for user-created documents which you might: A)save copies of for distribution, B) delete or modifiy, C)backup for archive purposes(like entries corresponding to calendar dates...
In this set-up, from time to time make copies of all your: Documents and System files.
Perhaps one easy way would be(I haven't tried it. any recommendations or suggestions?) using a hard drive duplicator - - or boot into the system with another OS(LiveBoot Linux distro's make sense) and access the Hard Drives(system install and software install, and documents) to copy them to media(CD's, DVD's, Blu-ray... other hard drives(used for backup only) or best of all, UFD's(flash drives).
Optical disks have been a pain for me as there are stupid naming conventions and 'folder depths' which interfere with copying...I don't think I've had any problems copying from NTFS to a UFD(I think the flash drive was FAT format...)
side note: if possible(without affecting performance or stability) upon a clean install consider installing applications onto a separate drive... many programs are highly customizable and are used in a way which their file creation takes place in the installation folder. In any event, my 'program files' folder contains many hundreds of MB of data, so much of which I depend on for my software's use.

Ideal(under my wild speculations) disk arrangement:
.)Fastest disk, size probably not more than 10GB?: Cache(swap file)

.)Faster disk(or same speed as above), size 4 - 15 GB for system only(maybe you have a higher GB demand than I...

.)Fast disk(or same as above two), size 10- 100GB, depending upon how many apps you install(maybe less than 10GB?).

.)'slower' disk(s), size 100 + GB(depending upon usage): storage of user files(backed up manually, loaded into/from such folders as "My Documents," "My Pictures," et cetera...

.) additional disk for more storage of documents, perhaps additional disks can be used for organization(one disk for videos, one for text; each disk tailored to the size needs for its content).
+) at the document level it might be better to have one 100GB hard drive for all document storage and from time to time(or daily or more frequently for the paranoid with a NAS) back up to other media from this HD

Leo villanizes RAID 0 saying it is a "bad idea" and a "serious risk."

WHY do we think a 0.2% chance of failure is so much worse than a 0.1% chance? Either way, we're talking about a fraction of a percent.

Odds are much better that a person will lose data due to user error, malfunctioning software, or malware.

The real bad idea here is to not have any backup plan.

Simcha Wachtel wrote:"file system corruption that is easily resolved by running scandisk from the Recovery Console"

[Cough, Splutter !]

My hard drive managed to acquire a crosslink, and when I used ScanDisk, I ended up with - wait for it - seventy THOUSAND "new" files ! The cross-link had destroyed my "Pictures" folder. So I still have the data - but as far as I know, I can't re-assemble it !

I use RAID 0 for 4 years and I am very pleased with the performance (speed) BUT I use a external HDD for weekly backup. If you think only at bad things you do not dare to cross the street.

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