Seriously Annoyed

[Funkstar]

Yes that would hold your drives, you would need four SATA cables leaving your PC to connect it up though.

The reason arthurleung suggested 3x 500GB disks was for backing up your data, not as a RAID array

[peterb]

But do you NEED raid - to repeat _It is NOT a replacement for backups_

Far better to have two drives (same size) one as an active system drive - the other one in a caddy and only on line when you do backups - that way it isn't in constant use (and therefore suffereing wear and tear) but will be an exact copy of your system lfrom the last time you backed it up! Even if you have RAID 1 or 5 - you will still need some form of backup in case the raid array becomes corrupted - RAID won't protect against that!

[neonplanet40]

SO your saying that i can just turn one on every now and then and it will automatically backup whatever is on the disk from the last time it was on? Is this a form of raid?

I also think i would need more than 2 disks as i have 1.3-4 TB to backup.

Neon

PS - Thanks for the help guys and sorry for the noob questions.

[Blitzen]

RAID won't protect against that!

Yes it will.

RAID 1+0

[neonplanet40]

Ok what now? Lol

[GSte]

For RAID 1+0 don't you need four times the storage capacity of the data your trying to protect, ie for one 500GB disk, you'd need four 500GB disks?

[Dreaming]

I think if you're after live-uptime then for the price, 3x500gb HDDs in raid5 will give you 1tb to play with. Then anything important (for me, I backup 30gb of un-losable documents and so on - I have loads more films etc. but it would be too costly to backup) backup to an external drive.

I'm still looking for the best software to do this, I was using ms windows copy which was ok but isn't brilliant at knowing what is new or not, so I have tonnes of copies of the same files. Apparently xcopy script does it quite nicely, but it's whether I can be bothered with the ins and outs. I have no doubt there is a freeware or cheap program out there that you can turn on, set up, then you just need need to click a big 'backup' button.

Raid1 for backups will not protect you against your PSU blowing up and taking out all your hard disks. It won't protect you against the raid card failing and corrupting your drives in a striped set up i.e. raid0, raid5, raid10. It's there for basic redundancy. I do use a raid set up for increased performance though.

In it's normal use, it's for something like a server that does regular daily backups. In that time though, if you're have lots of sensitive and important data coming in and out, and then there's a fault on a hard disk - you could lose all the data from that day. Not to mention the time required for restoring a backup. Whereas with raid1 or raid5, it would pop up an alert to the sys admin saying a drive has failed, and he could then go and replace it probably with a hot-swap rackmount taking him 2 minutes , which would then start to mirror itself automatically again.

Having said that, with the price of an external hard disk, how can you not afford to backup your cherished holiday pics, your contacts, your summaritive assignment and so on? I know if I lost photos accumulated on my hard disk from the last 3 years of my girlfriend and my relationship my life expectancy would get much shorter much quicker

£50 (Computer hardware and software at amazing prices, available online from Scan Computers UK) for life insurance? Bargain

[SiM]

For RAID 1+0 don't you need four times the storage capacity of the data your trying to protect, ie for one 500GB disk, you'd need four 500GB disks?

No you just need twice... Its like mirroring a striped Raid 0 array

[peterb]

Yes it will.

RAID 1+0

It won't protect against a controller failure, memory failure that corrupts the file system, or a power supply failure that destroys the disks. If corrupt data is written to a RAID array - it will be stored as 'correct' corrupt data. RAID only protects against drive failure. To the OS, the RAID array is a block device - how the data is stored across it is irrelevant to it)

Offline backups aren't automatic, how you do it is up to you. You could connect an external drive and do a bit by bit clone of the whole system, or you could use the windows backup utility and do full, differential and incremental backups. It will still need some time on your part. How far you want to go, how much time you are prepared to take depends on the the value you put on the data, the time taken to reconfigure the system in the event of a catastrophic failure and how much risk you are prepared to take.

As a worst case - your PSU fails and takes out the mobo, disk drives and processor. A clone of the system pretty much allows you to get up an running again easily. Buy new hardware, insert the cloned disk and thats it - no system re-installs or reconfiguration. Alternatively you may think that the system can be re-installed, so you could partition th esystem drive into two or three partitions, say one for system, one for applications, and one for user data - and just back up the user data partition - the frequency depends on how quickly the data changes.

But the decision comes down to you - the value to place on your stuff, the risks you are prepared to accept and the time you are prepared to spend getting your system back.

To illustrate my point - I run a web server with a RAID 1 array (mirroring) and I backed up 'sometimes' on the basis that hard drives are the most likely point of failure and hey - I had RAID. A Few weels ago I started noticing file system errors (its a Linux based system with an ext3 journalling file system) So I ran the fix disk utilities, and got all sorts of errors - until I ran it on the system disk and the system just crashed - and would not reload. The boot partition was OK, but after the intial sequence I just got a no system disk message. After a bit of investigation I found that the memory had failed and the corrupted memory had crashed the system, and (I thought) corrupted the disks. Actually, the kernel had crashed, and deactivated the logical volumes, and after investigating some data recovery firms (lowest quotes about £300 - £450, highest in the low thousands) I worked out what had happened and managed to reactivate the logical volumes and then repair the corrupted file system (lucky I was using a journalling FS). Although the webserver was up and running again after a week, it took another couple of weeks to get everything back as I wanted it.

Had I had a cloned system disk I could have been up and running within hours, and up to date with an incremental backup. I now have a tape drive as my backup store - my insurance policy which cost about the same as the low end data recovery specialist. With tape I can achieve the same thing in a more convenient (for me) format.

You may not need to go to such extremes - but if something unexpected can go wrong with a system - at some point it will!

[GSte]

No you just need twice... Its like mirroring a striped Raid 0 array

Ah right.....

[Dreaming]

You may not need to go to such extremes - but if something unexpected can go wrong with a system - at some point it will!

:yes:

A RAID does not protect against any of the following:
- small children
- beer
- small animals
- large animals
- the effects of beer
- family members trying to use your computer ("I thought typing sudo rm -rf / gave me internets )
- meteor strikes

I would recommend a good software package to manage backups but don't know any

[Saracen]

For RAID 1+0 don't you need four times the storage capacity of the data your trying to protect, ie for one 500GB disk, you'd need four 500GB disks?

You need a minimum of four drives, but in usable space, you get half the total capacity. i.e. four 500GB drives gives you 1TB.

The difference is in resilience, performance and rebuild time.

But you need to be very careful to be sure exactly what is meant when someone talks about RAID 0+1 or 1+0 because different people (and manufacturers) use the terms differently. The most common convention is that 0+1 means stripe then mirror, and 1+0 mean mirror then stripe.

Think of it this way. You have eight drives. What happens when you 0+1 and 1+0?

RAID 0 + 1 = stripe then mirror. Take half the drives (four), stripe data across them, then create a single mirror of that stripe. You have have a four-disk stripe, that's mirrored. Lose any disk in a stripe and you lose the stripe.


RAID 1 + 0 = mirror then stripe. Take a pair of drives, and create a mirror. Then take the next pair and mirror them, then the next and then the last. You now have four pairs of drives, four mirrors. Now, write a stripe across the first drive in each pair, which, of course, then gets mirrored.


Now think about failures. RAID 0 can't cope with losing any of the drives in that stripe. So under 0+1, if a drive fails, that entire stripe (four drives) fails, and you're left with the other stripe (of four drives). If another drive then fails in the other stripe of four, you've lost the entire array.

With 1 + 0, you have four mirrored pairs, and you need both drives in a single mirror to fail to take the lot down. Suppose the first drive in the first mirror fails - you've lost a drive, and some resilience. But you only lose the entire array if the next drive to fail is the other drive in that mirror. If you lose a second drive, you still have the array provided it's not the mirror of the drive that failed.

Both 0+1 and 1+0 can lose a single drive without losing the array. You know have 7 drives left running. If you lose ANY of the drives in the other stripe (i.e. 4 out of the 7 drives) you lose the entire array. But with 1+0, you'll only lose the array if the next drive to fail is the mirror of the dead drive (i.e. 1 specific drive out of the 7).

But it's worth noting that in EITHER case, a second drive failure might lose you everything on the array. This is why RAID is aimed at resilience (uptime) and sometimes performance, and is not so much a good alternative to a backup as a good supplement to one.

Of course, you can reduce the risk of data loss even further if you combine the parity capabilities of RAID 3, 5 with mirroring. With RAID 51, you can lose at least 3 and up to 5 drives from that 8 disk array without losing the entire array. It's extremely resilient, but the price you pay is it's inefficient capacity-wise. If that 8 drive array was 500GB drives, you'd get 1.5TB from your 4TB of drives.


This is not a complete account of benefits or drawbacks, and I've barely touched on performance benefits or rebuild scenarios - just the basic structures.

[Saracen]

Oh, and one more point - I've talked about multiple drive failures in the above post. Bear in mind that those failures can happen VERY quickly. A PSU failure could nail several drives simultaneously. Don't assume you'll necessarily have time to replace a drive and rebuild before the second drive fails. You might have weeks or months between drive failures ..... or milliseconds.

I did have such a PSU failure that cooked ALL the drives in a machine. So, perhaps you could then start thinking about iSCSI to get round that.

[neonplanet40]

To be honest i will be looking it back up my files in case of a DRIVE failure. Not currupt data. Seeing as the only problem ive seemed to have in 4 years is a drive failure, it is all im worried about at the minute. So what would be best for this? Just cloning?

My psu did blow a year ago but luckily it was a quality psu (im using another one of them now ie. enermex liberty) it only took itself out and saved every single bit of my hardware.

Mark

[GSte]

You need a minimum of four drives, but in usable space, you get half the total capacity. i.e. four 500GB drives gives you 1TB.

Thanks for all the info. Personally I'm not interested in RAID on any of my systems for some of the reasons you've outlined, plus the complexity of the thing, Acronis for me all the way!

[999tigger]

I have 2 spinpoints no problems at all with them fast and quite, just bought a third from scan.Hope it wasnt a faulty batch!

I back up documents to a pen drive.

If your disk still spins up then you can more than likely recover the data.