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Raid disc and auto system back-up

fotobits
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Registered: ‎23-06-2007

Raid disc and auto system back-up

Can a 2-disc Raid system be set up to enable D: to be mirror-image of C:.....C: being the system disc?
If so, in the event of mechanical or other failure of C:, can Windows then be opened from D:.....perhaps followed by changing the drive-name to C: ?
Regards.....
15 REPLIES
Superuser
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Registered: ‎30-07-2007

Re: Raid disc and auto system back-up

A 2 disc raid-0 ( mirrored ) system will only appear to Windows as one logical drive. In the event of a disc failure Windows will continue with the other disc as though nothing had happened.
fotobits
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Registered: ‎23-06-2007

Re: Raid disc and auto system back-up

Many thanks MisterW.
Or is the mirror-image state Raid 1?
If C: fails and the computer continues as if nothing has happened, does this include a normal closing-down and, later, a normal opening from Disc C:  ?
Regards.....
Community Veteran
Posts: 14,469
Registered: ‎30-07-2007

Re: Raid disc and auto system back-up

Raid 0 is stripped where both disks are combined to be a single disk. With say 2 x 300GB you get 600GB of disk. If one disk fails you lose everything.
Raid 1 is mirrored where the two disks contain the same data and are written to and read from at the same time. With say 2 x 300GB disks you only get 300GB of storage. If one disk fails the system continues automatically without the need to shut down as both disks always contain the same data.
You will either need a hardware raid capable motherboard (preferred) or you can use software raid, although on windows, software raid is not something I would recommend doing. You can buy SATA and PATA disk controller cards that support raid 0 & 1 if your motherboard does not support it.
If a disk does fail then you will need to shut the system down and change the failed disk. On start-up, certainly with hardware raid the new disk should be recognised and rebuild automatically from the existing one (you may need to identify it as a spare), and this can happen while you use the system. Many of the raid mobos come with aid software to manage your raid arrays.
Superuser
Superuser
Posts: 6,953
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Registered: ‎30-07-2007

Re: Raid disc and auto system back-up

Yep , sorry I meant raid-1, too much Christmas cheer...
fotobits
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Registered: ‎23-06-2007

Re: Raid disc and auto system back-up

Many thanks MisterW and Peter.
In particular thank you, Peter, for the recommendation regarding Raid hardware/software control......most valuable!
I think I'll ditch the idea of using Raid to back-up my C: system disc and create a disc-image instead!
Thank you both again.....Noel
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Registered: ‎14-07-2009

Re: Raid disc and auto system back-up

You may find that although many motherboards nominally support RAID, in practice it doesn't work work very well.  I've had poor results on an Nvidia chipset.  The RAID control software was not properly updated to the latest version of Windows (which was Vista at the time), the fact that the RAID array had failed was only in a message that flashed past you when booting the computer and I could never get it to repair.  I had essentially the same problem twice on two different computers (with similar motherboards).  Not to mention the fact that you have to set up the RAID array then install Windows, it cannot be established retrospectively.   
fotobits
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Re: Raid disc and auto system back-up

Interesting ReedRichards, I have Nvidia!
Many thanks for your comment.  I'm certainly not pursuing activating Raid.
Regards.....Noel
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Re: Raid disc and auto system back-up

I found the article here http://www.pugetsystems.com/articles.php?id=29 "Why RAID is (usually) a Terrible Idea" informative.
fotobits
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Re: Raid disc and auto system back-up

My goodness ReedRichards, quite a damning report.  However, what useful feed-back from such a relevant source.
Many thanks ReedRichards that's certainly set my position in the whole matter!
Regards.....Noel
Community Veteran
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Registered: ‎30-07-2007

Re: Raid disc and auto system back-up

Don't believe everything you read....
I can't see how the author came to the conclusions he did as the facts don't back it up. Plus he has not considered all aspects of raid arrays. RAID 0 has always been a no-no on it's own (see later)  as it more than doubles the chance of losing all the data on all drives in the array due to a single disk failure.
Why do you think most business servers use raid arrays - it is to mitigate against such single drive failures that the article is talking about - the chance in a raid 1 set-up that both disks would fail at the same time is very small. If you do go for just a single disk then if it fails you lose everything. Recovering from a single drive failure in a raid 1 set-up is far easier than having to recover all your data (assuming you do have a copy!) when using a single disk set-up. Also the remaining disk in a raid 1 set-up will have the current data and you would not loose any data, whereas recovering from a single drive set-up from a backup would only be a recent as the last backup so you lose any data since then to now.
Raid arrays can never be considered a reliable backup solution, you should always have off-system backs to tape or other disks. This is just common business sense - raid arrays would not help if your PC/sever were stolen!
He has also not considered the other benefits of a raid system - that is increased performance. Raid 1 can increase read speeds as the data is requested from both drives. Many raid systems have hot-spare drives which can automatically be used in place of a failed drive thus keeping data integrity. Now I realise this is probably beyond most home users due to the expense of additional drives being used but for businesses, where reliability of servers is vital, this is a small cost to pay.
I have used raid arrays for years and never lost any data using raid 1. Raid 5 is somewhat more problematic though due to the complexities of the architecture used so tend to steer clear of that method. If I needed to have a single file system beyond the size of available drives I would use a raid 1+0 set-up; 4 disks arranged as 2 x raid 1 with the 2 raid 1 arrays configured as raid 0.
A simple 2 disk raid 1 set-up for home use can have many benefits as long as you always remember that a raid array is not a replacement for adequate off-system backups of your data.
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Re: Raid disc and auto system back-up

Quote from: Peter
A simple 2 disk raid 1 set-up for home use can have many benefits as long as you always remember that a raid array is not a replacement for adequate off-system backups of your data.

Totally agree.
I think the problem is that many people have an inadequate understanding of what RAID is and does, especially the variants, and how to use it.
Personally, in a business environment, I've always used large-scale RAID5 with hot-swap and hot-spare drives - and never had an issue convincing management of the value of the (relatively small) additional up-front cost.
At home I have one system with mirrored drives via an onboard controller, but do understand its usefulness and limitations. I've had to rebuild it once in 2 years.
fotobits
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Re: Raid disc and auto system back-up

Very many thanks Peter and HPSauce.  I'm certainly learning a lot from this string!
Regarding a Raid 1 configuration, am I correct in assuming that Raid 1 covers you for mechanical disc failure, but not for any s/w failure/corruption?  Hence the necessity for a further backup, ideally external.
From the home-user perspective, the provision of security for documents, photographs and email folders is fairly straight-forward, cheap and quick.  In my case this is external and carried out daily.  It's the strategy for system security that's more challenging.
I've just implemented Ghost specifically to provide an image of C:\ on a second internal hard disc and hope this will relieve most of the agro caused by potential h/w or s/w problems.
If/when I renew my PC I will certainly make systems integrity an issue when configuring the h/w!
Thank you all all again.....Noel
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Re: Raid disc and auto system back-up

Quote from: fotobits
1 am I correct in assuming that Raid 1 covers you for mechanical disc failure, but not for any s/w failure/corruption? 
2 It's the strategy for system security that's more challenging.

1 Yes (essentially)
2 Most definitely.

For the latter it helps to think - how would I rebuild this system from scratch, assuming it vapourised.....
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Re: Raid disc and auto system back-up

Quote from: Peter
I can't see how the author came to the conclusions he did

It's there in black and white: "at the agreement of our support staff, I estimate that anywhere from 25% to 30% of our customers with RAID will call us at some point in the first year to report a degraded RAID array or problem directly resulting from their RAID configuration."  Now the author does not say what percentage of these clients opted for RAID 0, which I agree is just asking for trouble, but even so
Quote from: Peter
Why do you think most business servers use raid arrays - it is to mitigate against such single drive failures that the article is talking about

Actually, the reason is that they want to keep going in the event of a single drive failure and then make repairs at a convenient opportunity.  Using RAID doesn't mitigate against single drive failures, it mitigates against the immediate consequences of a single drive failure, which is work grinding to a halt.
But you are missing the point!  What the article says quite explicitly is " all (yes, all) RAID controllers onboard a motherboard are low quality".  Servers do not use motherboard-based RAID controllers, they use proper expensive ones.  "A good [hardware] raid controller starts at $300. If you have a RAID controller on your $150 motherboard, what does that say about the quality?".