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Setting up a RAID (mirror) to avoid data loss

Setting up RAID
The description below is for setting up RAID on your EXISTING computer. For setting up a BOOTABLE (C:) RAID system on a NEW computer, see my Guide to PC Security, RAID setup on a new PC page.

Note - below assumes your computer is running either Windows 2000 or Windows XP. If you have Vista, I suggest you check with the manufacturer if your computer can be upgraded to XP :-)

What's RAID (and what's 'mirror') ?

RAID** is a way of duplicating your data across multiple disks so that if any ONE disk fails you can replace it without loosing any data. The most basic type of RAID is 'mirror' = it uses 2 drives that are configured to contain identical data = i.e. the data is 'mirrored' (duplicated).

**RAID means "Redundant Array of Inexpensive Disks". RAID-1 means 'Mirror' and RAID-5 means 'more than 2 (mirror) disk RAID'. You will also see 'RAID 0' = this means NOT RAID (it is simply all the drives added together as a single drive letter so when one fails, you loose the whole lot, with no hope of ever getting anything back, hence the other name 'JBIG' = Junk Big :-) )

Since all drives in a RAID system must be the 'same' capacity, any extra space on any drive(s) larger than the smallest drive in the 'set' will be ignored.

What's the drawback of RAID ?

A1. The data capacity of the system is always one disk less than the number of disks in the RAID 'set'. So in a 'mirror' (2 disks) you are limited to the capacity of one. In a 3 disk RAID, the usable capacity is 2 disks & in a 4 disk system it's 3.

This is because a RAID system has to survive the failure of any one drive. So it must be 'formatted' in such a way that 'one drives worth' of data is duplicated. This limits the total user space available to 'one drive less' than the total drive count.

A2. You can build a RAID system with 'any' number of disk drives, however whilst a 'mirror' is easy to implement in software (with almost no impact on performance - indeed READ speeds may actually 'double'), a RAID system with 3 or more drives really needs a dedicated Hardware interface

The more drives, the more complex the RAID format gets. PCI RAID cards are typically limited to a maximum of 4 drives (although most let you configure these as you see fit - i.e. as a 4 disk RAID-5 or as 2 pairs in a RAID-1 mirror)

A3. One drawback that gets little mention is what to do when you outgrow the capacity of your RAID system ? Plainly you have to get the data off your existing 'drive set' and onto a new, bigger drive 'set' - at which point the number of drives supported by your system becomes key.

With RAID-1 mirror system, all you need to do is 'break' the Mirror and replace one of the old drives with a new, larger, one. After copying everything from the remaining old (small) drive to the new (bigger) one (using a combination of Cloning (for the Factory Restore partition) and file copy (using DriveImage XL or similar), you can replace the second old drive with another new, bigger, drive.

After re-booting, you just 'rebuild' the Mirror. This is explained in detail below (see 'increasing the size of your C: Mirror')

With a 3 or more disk RAID system, it all depends on how 'clever' (read, 'expensive') your PCI RAID card is. 'Clever' cards will allow you to replace one drive at a time with a larger one (until you have a complete 'set' of larger capacity drives) and then let you 'expand' the RAID to make use of the extra space.

Less clever (i.e cheaper) PCI cards won't offer the vital 'expand' function .. which will more or less force you to install a second PCI RAID card, build the larger RAID set on the new card and then copy everything across (this is not necessarily a problem as drive technology and capacity increases, chances are your old SATA II / 2TB limited RAID card will have to be replaced with a SATA II / 6TB+ card anyway)

What Hardware is compatible with RAID (mirror) ?

Any desktop or tower PC with room for at least one more hard disk, of course :-)

It is (just) possible to setup a SFF (Small Form Factor) box with a RAID Mirror C: - and even the larger laptop (with built in CD/DVD) - however the CD/DVD drive has to be replaced by a second hard drive (which means using an external USB case for the just removed CD/DVD drive)

How many new drives do I need ?

A1. If your computer is not too old, the cheapest and simplest approach is to purchase one new drive similar** to the C: drive you already have.

**all you need is one of the same (or higher) capacity = so don't go paying rip-off 'spare part' prices for an 'identical' (Dell / HP) C: drive

A2. If you have an older computer or a 'self build', I highly recommend that you purchase a pair of new drives and save your existing C: drive 'for emergency use only'. If your computer case has room for a 3rd hard disk, you could use your old C: as a 'local backup' drive (you should avoid using it for 'live' data because it won't be part of the Mirror).

My approach to creating a system C: RAID requires new drives of at least double the capacity of your existing C: drive (if less, you can still use them to make a new Mirror D: drive).

Converting an existing running system on a low capacity C: into a higher capacity C: RAID is quite complex, however has the advantage that, after the first step, you can always plug your old working C: drive back in and go back to 'try again' if anything goes wrong.

A2. The Windows XP disk capacity limit is '2.2Tb' (2048 GB) - larger drives can be used but only the first 2048GB can be configured as a RAID mirror using XP's built in RAID support

A drive can be configured to over 2048 GB using the Hitachi GPT disk manager, however this utility / driver does not support RAID capability

Do I need a spare PCI slot for RAID ?

A1. No, not for Mirror. All versions of Microsoft 2000 and XP contain support for software RAID (although it is only enabled on the Server versions) and this is perfectly adequate for running a RAID Mirror.

Using software to support RAID 1 works just fine. When writing to a Mirror, the CPU only has to sends two write commands to two different drives, telling them to DMA the exact same data from the exact same RAM locations - and then wait for whichever finishes last (both drives being equal, they should finish at much the same time).

Reading from a Mirror, however, can be done almost 'twice as fast' !

The CPU asks the first drive for the first block of data, and, whilst that drive is busy, it can ask the second drive for the second block (in practice, the CPU will send read commands to whichever drive it thinks is going to deliver the data first - which depends on 'where the data is' (on the drive surface) plus how big the current 'queue' for that drive is)

A2. Yes, for RAID-5. Whilst Windows 2000 and XP software also support RAID-5, few motherboards support more than 4 disks (of which 1 will be your CD/DVD drive) and using software to support a RAID-5 will result in a noticeable slowing down of your system.

Making a PCI RAID system 'bootable' (i.e. as C:) introduces more complexity, so I suggest using RAID-5 only for data storage

What additional software will I need to setup software RAID mirror ?

A1. To edit your system config. files, you need the Open Source Hex Editor utility.

A2. The simplest way to copy your C: disk is using Clonezilla Live ISO (download and burn** to CD).

Unless your computer is a 'build it yourself' or is Windows 2000 based, chances are you will have a hidden 'factory restore' partition on C: and Clonezilla is the only way to copy this to the new drives.

**If you don't already have ISO burning software, I recommend ImgBurn. Note this is entirely free for non-commercial use, however I would like to encourage you to make a donation to the author - he is only asking for $2 and this software beats all the commercial rubbish (such as the Nero, Roxio, Digital Media Studio, Sonic or the Sony (DRM infected) 'free trial' that was, no doubt, 'included' with your new computer) hands down.

A3. If you are replacing an existing C: with 2 new, higher capacity drives, and you want to increase the size of your C: drive, you will also need DriveImage XML.

If I have Clonezilla, why do I need also DriveImage XML ?

DriveImage will copy your system to a new drive using a file copy process leaving the size of the partition on the new drive intact. Clonezilla will overwrite any partitions on the new drive, so is unable to make your C: system any bigger even on a higher capacity drive (although the extra space can be used as D:).

If you are using 2 new higher capacity drives, but are happy to leave your C: the same size (and use the extra space as D:), you can avoid one extra step in the setup (and won't need DriveImage XML)

Is there anything I need to do to prepare my PC system first ?

A1. Yes, you must install the Windows Recovery Console (if you don't already have it). To enable RAID you will have to make changes to 3 of your System files. You will need to boot into the Recovery Console to replace the existing System files with the modified versions.

When you power-on and the 'Choose an Operating System' list appears, one option you should have access to is the "Windows Recovery Console". If you don't see 'Choose ...', go into root of C: and find the boot.ini file and edit the [boot loader] section to include 'timeout=5' (for a 5 second timeout). If you still don't see the Recovery Console option, you will have to install it from your Windows XP System CD. Fortunately, Microsoft does a good job of explaining in How to install the Recovery Console.

A2. Power-on into BIOS Setup and make sure that all your SATA drive interfaces are set to 'enabled' (or 'auto').

If you have room for 3 or 4 hard disks in your desktop/tower, your motherboard should have 4 SATA. However older SFF (Small Form Factor) boxes may have two SATA interfaces plus one IDE master/slave but no room for two hard drives. A bit of metalwork should allow you to replace the 'slim line' CD/DVD and floppy disk with a second hard drive (you can use an external USB case for the just removed IDE CD/DVD drive)

A3. To boot from the Clonezilla 'Live' CD, you must make sure the BIOS is set to boot from CD/DVD first

Old SFF boxes with no USB boot capability will have to be 'set up' with the lid off (so you can plug in the IDE CD/DVD drive to boot)

How do I add my new hard drive(s) ?

Open up the computer and find the SATA connections on your motherboard. Chances are 2 will be in use (existing C: hard drive and CD/DVD) - just plug the new drive cable into the first free SATA connection.

It's a good idea to mark the C: drive cable in some way - if you confuse it later you risk wiping your existing system !

If you have 2 new drives, install only one now (DO NOT add both at this stage). After installing the new drive, power-on into the BIOS and make sure it can be 'seen' OK.

Your existing C: will be 'disk 0', your CD/DVD 'disk 1' and the new drive 'disk 2' or maybe 'disk 3'. If it's 3, to avoid confusion later, I recommend you power off and move it's cable to the other free motherboard SATA connector now.

How do I prepare my (first) new drive for RAID Mirror ?

Boot using Clonezilla and use it to do a 'drive copy' clone of your existing C: drive onto the newly installed drive.

You should expect your original C: to be 'disk 0' (and contain at least 2 partitions), your CD/DVD to be 'disk 1' and the new, unpartitioned / unformatted drive to be 'disk 2'. If you see something else, be VERY CAREFUL before proceeding (if your mix up C: and any new, empty, drive you will end up 'cloning' 'empty' onto C:).

If you purchased a single drive similar to your existing C:, you can skip the section below and proceed directly to setting up your System Files for software RAID

What next if I'm moving C: to a pair of higher capacity drives ?

FIRST, remove your old C: drive and replace it with the just 'cloned' new drive. THEN confirm all is well by BOOTING INTO WINDOWS.

Then shut down, install the second new drive and use Clonezilla to clone the new C: onto the new empty drive.

If you are NOT CHANGING the capacity of your existing C:, you can then proceed with setting up you software RAID below.

How do I change the capacity of C: to use the new drive space ?

1) Go into Disk Manager and find the new drives - they should be C: and D: Each should have 2 partitions, the 'hidden' and the 'clone' of the old C: plus 'unpartitioned' space at least equal to C:.

If the unpartitioned space is not equal or larger than C:, you can't safely increase C: so just skip to setting up RAID mirror

Boot up into Windows. In Settings, Control Panel, Administrative Tools launch computer Management. Then double-click Disk Management. Check that it can 'see' both drives (disk 0 and 2) OK. The first (disk 0) should show as C: (the second may show as E: or just 'un-named')

The System Restore partition should be 'visible' to the Disk Manager as the first partition on the each drive. It will usually be shown as 'Healthy (Unknown Partition)'. It will typically be 3 to 5Gb in size.

2) On D:, delete the 'working' partition (which contains a copy of old C: = i.e. NOT the System Restore 'hidden' partition). You will now have one C: and one 'empty' drive.

Why do a 'clone' to D: if we are going to 'delete' the working copy ? Because the 'clone' is the only way to get the hidden 'system restore' partition onto the new drive

3) On C:, use the spare space to make a new D: that is equal or greater than C:. Quick Format as NTFS

4) On the empty drive, make a new 'Primary' partition (E:) - this will become be your new C:, so make the size you want. Mark the partition 'active' & format using NTFS.

5) Install DriveImage XML. 'Save' C: to a file on D:. Restore the file on D: to E: Don't bother using any sort of compression (unless you want to wait whilst it runs overnight).

DriveImage won't save (or restore) a partition to itself nor to a partition smaller than the 'source'. Hence save to D (which must be at least the same size as C:) and restore to E.

DriveImage makes use of Windows built-in 'System back-up' components known as "Volume Shadow Services" (VSS) & Volume Shadow Copy. Chance's are you have disabled some of the Services these rely on - so if you have trouble running DriveImage, check what services it needs :-)

6) Power off, unplug the cable from C: & plug it into E: (leave C: unplugged for now). Boot up into Windows to make sure all is working OK = E: will become the new, higher capacity, C:. If it fails to boot, check you made a PRIMARY, ACTIVE partition - then get out your Windows System CD and do a 'repair'

7) Once you have a new C:, plug in the other high capacity drive and use Clonezilla to 'clone' your new working C: over the 'smaller' version on the other drive.

8) Finally, boot-up to check you have a working system with two identically configured drives.

Why all the mucking about with C: > E: etc ? Well, if anything goes wrong, this way you will always have a 'working' / 'bootable' C: that you can go back to.

How do I setup Software RAID (mirror) ?

Get the full instructions for the modification (of Windows XP with sp3) which can be found at How to enable RAID in Windows XP Pro.

Similar instructions exist for Windows 2000 Pro and Windows XP-sp2

Locate the 3 system files and copy them to the 'root' of C: (it's a good idea to copy them twice - once to root and once to a folder in root called eg 'sys_old')

Now use the HEX EDIT tool to make the changes on the copies.

How do I replace my existing system files ?

Boot your PC into Recovery Console Mode (DO NOT allow it to boot into Windows) and replace the 3 existing files in C:\Windows\system. Make sure you also replace the versions hidden in the 'System Restore' folder (in c:\windows\system32\dllcache) otherwise, when Windows detects the changes it will replace your modified files with the old 'back-up' copies.

The Recovery Console is intended to allow you to 'boot' into a 'Command line' (DOS like) system even when Windows itself is so corrupted that it fails to boot. You can then use the Console to replace corrupted system files (by extracting them from your Operating System 'sliver master' CD), or, if unable to Repair your Windows, you can use the console to copy any vital data files off the disk before wiping it with a reformat whilst reinstalling Windows (or doing a 'factory restore', which has the same effect).

If it turns out you have mucked up the Hex Edit, you can use the Recovery Console to change the system files back (from the second copies in 'sys_old').

Be aware that if you ever have to do a 'factory re-install' (or re-install from the Microsoft Operating System CD), you will loose your software RAID - so it might be a good idea to 'burn' a copy of the modified versions on a CD-R (along with all your Drivers etc.)

Note also that how to enable RAID was discovered prior to the release of XP Service Pack 3. When sp3 was released, Microsoft replaced all 3 files with new versions (which then had to be modified slightly differently).
This MAY have been a simple co-incidence, however if your RAID suddenly stops working, the FIRST thing I suggest you do is uninstall the most recent MS Update :-).
NB. A similar approach may allow Windows 7 Home 'premium' users to access RAID functionality (it's enabled by default in Win7 Pro and 'above').

How do I build the Mirror ?

Unfortunately** you have to 'convert' both disk 0 and 2 to 'Dynamic' mode before Microsoft will allow you to build the RAID.

1) Select (click on) 'Disk 0' and right click to choose 'Convert to dynamic'. When the 'convert' menu opens, select Disk 0 and Disk 2,l 'Apply' and reboot when asked.

**Dynamic disks seem to have more data transfer failures / corruption problems than 'Basic' disks. This may be due to the multitude of MS 'Services' that attempt to keep 'track' of file locations .. fortunately most of these can be disabled (you should have done this already - if not, see How to disable useless services).

2) After power-on wait whilst XP completes the 'Converting to Dynamic' sequence. Then, back in Disk Management, select Disk 0, right click and choose 'Setup RAID Mirror' and select disk 2 as the 'second' drive.

What if 'Setup RAID Mirror' option is 'greyed out' (un-selectable) ?

Chances are, your modified system files have been 'spotted' by Windows File Protection and 'restored from backup'. Go back and check you have made the changes correctly & then try again

Note that Windows 7 Pro (and above) enables RAID by default.
Note also, it's only possible to Mirror the 'unallocated' space on two (blank) drives (the Mirror option is 'greyeed out' unless 2 drives with unallocated space esists).
This means it's not possible to 'upgrade' an existing single disk to RAID by adding a second disk = you have to move your data to a 3rd disk first and then delete the existing partition(s) = as usual, the first step in any "Microsoft way" means wiping all your data ...

NOTE - you can disable Windows File Protection (WFP) from Safe Mode. From Start, Run, type 'regedit' (or regedt32).

Find the registry key [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon].
In the right hand pane, 'Modify/Add a New DWORD Value', right click & enter name as 'SFCDisable'.
Then enter a value of 'ffffff9d' (Hexadecimal) to disable WFP.

When you next boot-up, the changes will take effect (after which you can delete the (hidden) folder C:\ WINDOWS\ system32\ dllcache\ which contains about 300Mb of duplicate (and unwanted) system files).

You may have to disable WFP later, anyway, before Windows allows you to strip out some of it's more useless hacker friendly (and thus unwanted) services and applications.

Click 'Next >>' in the Navigation Bar (left) for my guide on formatting drives over '2.2Tb' for use with XP or click here to go straight to my Backup & Synchronisation page

The pages in this topic are :-

  + Hard drives over 2Tb - (with Windows XP) == Latest changes (modified 24th Jan 2017 07:46.)

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