Can someone explain in plain English what RAID 1 is? (1 Viewer)

[do re meep meep]

A hard disk of mine crashed, fortunately there is a back up on an external disk, unfortunately the data restoration turns out to be a pain. I want to do things better if it happens again, and I heard about disk mirorring with 2 disks and RAID 1, but cannot really understand the explanations that Wikipedia provides, see below.

What do I need to do to implement the disk mirroring? Obviously, I need 2 disks. Can I install the second disk in a PCI slot/card? How do I tell Windows XP to mirror the two disks?
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RAID 1: Mirrored Set (2 disks minimum) without parity. Provides fault tolerance from disk errors and single disk failure. Increased read performance occurs when using a multi-threaded operating system that supports split seeks, very small performance reduction when writing. Array continues to operate so long as at least one drive is functioning.
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Software RAID
Software implementations are provided by most operating systems. A software layer sits above the (generally block based) disk device drivers and provides an abstraction layer between the logical drives (RAID arrays) and physical drives. Software RAID is typically limited to RAID 0 (striping across multiple drives for increased space and performance), RAID 1 (mirroring two drives) and RAID 5 (data striping with parity).

In a multi-threaded operating system (such as Linux, FreeBSD, Mac OS X, Windows NT/2000/XP/Vista and Novell NetWare) the operating system can perform overlapped I/O, allowing multiple read or write requests to be initiated without waiting for completion on each request. This is the capability that makes RAID 0/1 possible in an operating system. However, most operating systems do not support RAID 0/1 striping or mirroring with parity, due to the substantial processing demands of calculating parity[citation needed].

Software implementations require some very small amount of processing time, which is provided by the main CPU in the host system. Since SCSI, PATA, and SATA drives all support asynchronous read/write, any multi-threaded operating system can support non-parity RAID on multiple hard drives with only a one percent increase in CPU overhead[citation needed].

Software implementations can exceed the performance levels of hardware-based RAID due to the high-performance of modern CPUs[citation needed]. Since the software must run on a host server attached to storage, the processor (as mentioned above) on that host must dedicate processing time to run the RAID software. Like hardware-based RAID, if the server experiences a hardware failure, the attached storage could be inaccessible for a period of time.

Software implementations can allow RAID arrays to be created from partitions rather than entire physical drives.

 

[rozinante]

I am not familier with the specifics of XP's RAID handling myself but there is a step by step guide here:-.

http://www.duxcw.com/digest/Howto/mb/abit/kx7-333/raid1.htm

In general though I think you will find that much of the considerations and complications around the different RAID setups relate primarily to maintaining max performance of servers. If you have a small lightly loaded network or a standalone pc, RAID 1 should be fine.

 

[rozinante]

Just noticed that the link above relates to setting up an on board RAID controler. You don't say if your board has an onboard controler and if not you will need to use software RAID.

This link may help:-

http://www.techimo.com/articles/index.pl?photo=149

 

[do re meep meep]

Thanks for the comments! I have nothing but a normal desktop computer (a workstation, not a server) with one hard disk and Windows XP Home. What is the simplest way to install a second hard disk to mirror the one I already have? I don't care whether the mirroring is done in hardware or software.

 

[djaburg]

What you're most likely want to do is determine what capability your motherboard has. I'm sure what your level of knowledge is, so I'll try to keep it simple. Your motherboard is the large circuit board in your computer case that everything else hooks up to and where your CPU (Processor) and your RAM (memory) is plugged in to. It's the heart of the computer. Many motherboards have the native ability to support RAID level 0 (striped) which is NOT good for data security or RAID 1 (mirrored) which IS good for data security. Setting up a RAID 1 array can be tricky with an pre-existing installation since the operating system will view the RAID array as a new "drive" and may not boot from it easily, however, there is a way around that. If your motherboard doesn't support RAID natively, then you'd need to get an add-in card that supports it. I've used both LSI and Promise add-in cards with good success. I DO NOT recommend running a software based RAID solution as they are inherently unreliable, especially if your data is critical to your business or you have important files.

What RAID effectively does is writes the same identical data to two drives that are treated as a single drive by the operating system. For example, if you have 2 80GB drives, you'll only have 80GB available to use, since both drives will contain the exact same data. If one drive fails, you'll be notified, but you won't lose any data since the other drive contains the same thing.

To set it up on an existing system, you'd need to shutdown the computer and install the add-in card (if you need one) and then plug the HD's to the RAID controller. IT IS VERY IMPORTANT THAT YOU ARE ABSOLUTELY SURE WHICH DRIVE HAS WINDOWS ON IT BECAUSE IF YOU DON'T YOU MAY LOSE EVERYTHING YOU HAVE INSTALLED DURING THE CREATION OF THE ARRAY. You then need to make sure you have a driver disk (floppy) with the correct drivers for your version of windows. Normally when you boot after installing the card and plugging in the drives, you will see a new screen during the initial boot process where the RAID controller initializes and you have the option to configure the array. This is where you determine your "source" disk, in other words the disk that has windows on it now. The array will then be "built" copying/mirroring everything on the source drive to the other one. At this point you're still not out of the woods, because now you have to get the drivers in to windows and also tell windows where to boot from. I recommend using the in-place upgrade/install as instructed by Microsoft. During this process you need to use floppy with the drivers to get the controller recognized by windows. The most important thing is not to panic when windows initially boots as you will get error messages UNTIL you install the windows updates you had previously installed.

 

[do re meep meep]

I'm sure what your level of knowledge is, so I'll try to keep it simple.

It sure doesn't help my ego, but you sure got it exactly right! 3

Anyway, hardware RAID 1 it is. Now, I have a Dell E521 in its very basic configuration http://configure.dell.com/dellstore/config.aspx?c=ca&CS=cadhs1&l=en&oc=E521SB_R_E I am thus hoping that its motherboard supports RAID 1 natively not requiring any add-in cards (are these PCI-cards?) But somehow I got to install a second hard disk! In a free slot of the bay perhaps? Does the second hard disk have to be identical to the one I already have?

My Windows is on the C: drive. If I install a second hard disk will it not be automatically designated the E: drive? The optical drive is now the D: drive. I don't have a floppy drive, can I use the optical drive for installing the RAID 1 drivers for doing the mirroring thing?

 

[djaburg]

When RAID is configured, you will only see one HD (would be designated C: since it's the first and only drive in the system) because RAID takes two drives of the same size and mirrors them, effectively making it one drive. As for your computer supporting RAID natively, I don't think it does. If you check here or perhaps here to see a few different models of PCI SATA RAID cards.