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Beginner RAID Question - Page 4

post #31 of 35
Quote:
Originally Posted by CasanovaFly View Post
@beers: So my system would refuse to boot until I solved the problem? Which would be to properly hook up my hard drive again? Is it kind of like a failsafe for my operational stupidity can't harm it?
Not really.
RAID 0 with two drives saves half of the data on each drive.
Every file and chunk of data gets split up into 64k or 128k stripes between drives.

If you don't have one drive, you have random stripes of half of your data, and would not have anything coherent. Based on this, there's no way for you to access any of the files or boot the machine's OS.
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post #32 of 35
Quote:
Originally Posted by parityboy View Post
RAID is NOT a backup, but some RAID schemes will tolerate a certain level of disk failure in order to maintain uptime. RAID makes no guarantees of data integrity or data security, only system uptime.
This.

Quote:
Originally Posted by Tator Tot View Post
Calling it a back up is much easier for some to understand.
But it isn't backup. So you haven't helped him to understand, you have confused him further. He just doesn't know yet.

Quote:
Originally Posted by CasanovaFly View Post
I know that RAID doesn't back up data, but I know that it gives you somewhat similiar securities, in not so many words.
That right there is the problem. It doesn't give similar security at all. But as you have been led to believe it does, you are happy thinking your data is safe. Sadly it isn't. RAID will help your data remain accessible if a drive fails. But that is all. It won't help for the most common way to lose data - user error. If you delete something (or format the wrong drive etc) then it's gone. With a backup it isn't. Now you may laugh and think 'How stupid - I won't do anything like that'. But I will guess you've done it before (ever saved over the wrong file?), and will put money on you doing it again in the future.

RAID also won't help with other data loss causes like fire, theft, flood, software corruption and viruses or hardware failures such as PSU faults (or something as stupid as your dog knocking the case over or your kid pulling out a wire. Backups can protect you against all of these things.

Quote:
Originally Posted by parityboy View Post
RAID is NOT a backup, but some RAID schemes will tolerate a certain level of disk failure in order to maintain uptime. RAID makes no guarantees of data integrity or data security, only system uptime.
Just to illustrate again - RAID isn't a backup. RAID protects your arrays, not your data.

Quote:
Originally Posted by Tator Tot View Post
Software RAID generally has a huge system overhead and is slow. (This is not the case when using Linux's software RAID.)

Motherboard RAID is sometimes called "FakeRAID" because it doesn't use a dedicated card. This isn't true though, as it is as real as a "Hardware RAID" solution which is on a dedicated card.

The other poster is talking out of their bum. The only reason a SB would have the RAID fail out like that is a bad BIOS or inadequate cooling around the Southbridge. Which is really hard to do as they are only 4w chips.
Sorry but it is you who are wrong here - obviously you don't have enough experience of RAID systems generally to make these kinds of statements. Some of us do this kind of thing for a living you know...

Software RAID - doesn't generally have huge overheads at all. Decent software RAID systems can outperform even the best hardware systems in fact. Even software RAID under Windows can perform decently. In fact the worst RAID5 performance you are likely to see will almost certainly come from a fakeRAID controller (which are in no way as real as a hardware controller - there are important differences which make a HUGE difference to your data availability). For example fakeRAID implementations often mess about with full stripe re-reads/writes on partial stripe writes when a better implementation just does a single strip & parity read then rewrites just that data - and knows when to do this and when to do a full reread for better performance. To state that they are as real as one another kinda points to you just not knowing or understanding the differences.

And regarding the southbridge - the problem here is that you have completely ignored the fact that it isn't the southbridge that's doing the RAIDing. It's the drivers - and they are (pretty much without fail) terrible at anything other than perfectly normal day to day activity. Which means if anything ever happens (a drive takes a little longer than normal to respond, you encounter a bad sector, the parity and data don't match etc) the fakeRAID freaks out and the array drops. And because these are consumer-level systems where RAID is basically added as an afterthought so the marketing guys have something extra to write on the box, there are really no tools available to recreate the arrays properly, so your data is gone. All gone. FakeRAID arrays can and do drop out with little or no reason, even though the SB is working perfectly. You may come back and say 'well I've been running an array for 20 years with no issues' - but that's not a lot of evidence is it? Search around - the vast majority of RAID problems you see involve fakeRAID parity arrays (note that running RAID1 or RAID0 on a motherboard is generally fine - these are much simpler to implement, and don't involve any of the complexities required for RAID5).

Quote:
Originally Posted by CasanovaFly View Post
Yes, 4TB is a lot of risk, but it's ONLY HD movies; WMV-HD files to be specific. If I lose 'em, I lose 'em. Life goes on. It's nothing that I couldn't replicate with a little time and effort. Though your queries do give me the desire to create a running list of what I've got just in case.
If it's just movies you have, then single drives would almost certainly be a better bet than RAID. That way if a drive dies you only lose *what was on that drive*. Everything else stays intact. For a little protection against drive failure you can then run a parity-based protection scheme like unRAID or FlexRAID that adds a parity drive (like RAID5), but doesn't stripe you data across drives (unlike RAID5). And that can be a lifesaver - it you have 10 2TB drives of ripped BluRays and 2 of them die, would you prefer to re-rip all 8TB worth (as you would need to if your data was in RAID5), or 2TB-worth as you would with the parity schemes? If a single drive dies then you are protected the same in either case (although the RAID-is-not-backup section still applies here to some degree - although I believe unRAID and FlexRAID will both allow you to recreate deleted files if you catch it quick enough...).
post #33 of 35
Thread Starter 
Quote:
Originally Posted by beers View Post
Not really.
RAID 0 with two drives saves half of the data on each drive.
Every file and chunk of data gets split up into 64k or 128k stripes between drives.

If you don't have one drive, you have random stripes of half of your data, and would not have anything coherent. Based on this, there's no way for you to access any of the files or boot the machine's OS.
But if the RAID does not have my OS on it, then what? Will the computer still boot?

Quote:
Originally Posted by the_beast View Post
That right there is the problem. It doesn't give similar security at all. But as you have been led to believe it does, you are happy thinking your data is safe. Sadly it isn't. RAID will help your data remain accessible if a drive fails. But that is all. It won't help for the most common way to lose data - user error. If you delete something (or format the wrong drive etc) then it's gone. With a backup it isn't. Now you may laugh and think 'How stupid - I won't do anything like that'. But I will guess you've done it before (ever saved over the wrong file?), and will put money on you doing it again in the future.
Come on now guys, I'm not completely daft. I don't know how a RAID works (parity, striping, blah) but I know what it does. I know that with my RAID, if one drive dies, I'm toast. I also know that other RAIDs have extra disks in case something happens to one of the disks. Your data is not backed up in that if all the disks die, you're boned, but there's still the opportunity to protect the data if one of the, say, four disks dies. And yes, I've deleted my fair share of files before. It happens. And will continue to happen.

The bottom line is that I don't have the financial means (nor SATA ports) to buy 2 more HDD's for everything than is necessary and I don't have the cash to drop on a littany of external backups to protect all my data. I am aware that mechanical hard drives fail. I'm going to assume the failure rate is rather low, though, and like all other users I'm going to take the risk. It's not a big one, but it's a risk in and of itself. I backup what I need to and can, and if a drive fails and I lose some stuff then I guess it just wasn't meant to be.

Thank you for the info on software RAID vs. hardware raid. I'm really only looking at RAID 0 though. The only reason I'm really doing it is because I want all my particular movie files on one drive, and I'm not dropping the cash on a 3TB. I stream them to my Xbox for playback and I don't want two different folders that show up saying "HD Movies". This is really the only reason I'm interested in RAID'ing. I'm particular about certain things. It also helps me with keeping my computer organized.
post #34 of 35
Quote:
Originally Posted by CasanovaFly View Post
I'm really only looking at RAID 0 though.
That right there is your problem. If ANY ONE of your drives die, you WILL be re-ripping ALL of your movies. ALL of your data will disappear.

If you just want all your movies to show up in one folder then junctions (mapping one drive so it appears as part of another drive) would be a better bet. That or using unRAID or FlexRAID to protect your data instead.
post #35 of 35
Thread Starter 
How do I do this junctioning?

And what is unRAID or FlexRAID?
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