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Hardware Thread, RAID 5 Mirror in Technical; ...
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    ozydave's Avatar
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    RAID 5 Mirror

    HI

    I have a Proliant ML150G2 with 4 160Gb drives in a hardware raid 5. (it is our main domain controller – we do have a backup domain controller)
    The array have been split into 3 so the c (system) partition is part of the raid 5. Not ideal I know, it was already setup when I got here.
    I want to get a mirror of the system partition (c Drive).
    What is the best way? Can I just add another dive and then use windows disk manager to mirror c:
    Will it work if I attach an external hard drive and then use windows disk manager to mirror c:

    Fairly new to RAID so not sure what the best method is – I don’t want to start from scratch

    Many Thnaks

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    DMcCoy's Avatar
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    I would suggest that unless you are experiencing extreme performance problems that you leave it as it is. There will only be light load on that partition for the DC functions and moving it will be quite a lot of work. You will need another pair of disks, and hope that you can create a second raid volume with the raid card in the server. Then you would have to mess about with imaging and wiping and resizing everything to get it in the right place. You do *not* want to add a software mirror of a volume that is already part of a physical raid set.

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    mattx's Avatar
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    Why would you want to mirror a partition when its already striped over the 4 drives ?

    Will it work if I attach an external hard drive and then use windows disk manager to mirror c:
    The RAID is not hardware controlled then ?

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    greenfieldsupport's Avatar
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    It will be Hardware RAID as its A. a HP and B. Windows doesnt support S/W RAID 5.


    DO NOT add a usb hard disk and use software mirroring as it will reduce the whole array down to the speed of your USB hard disk, as it will be forced to write to that and your "C drive" area of your Raid array

    The way the array works is:
    The 4 drives will create one LARGE contiguous space.
    1 of the drives will be used for parity, so with 4 160gb drives you will be left with (3 x 160) 480 GB to use (less than this when formatted.) Windows will see this as one big huge fat drive which can be partitioned.

    If a disk should fail, the speed of the RAID array will slow down as the computer will have to access 3/4's of the data from disk and work out the remainder using parity calculations.

    at this point you would insert a new disk, and the server would rebuild the data on the disk that died onto the new disk.

    A Raid array will be FASTER than 4 single hard disks working independently at reading, however it could possibly be slower at writing as your computer has to compute the parity of every file written, so this is dependent on how hardware based your RAID controller is and how big the processors are


    Im wondering what your trying to do? what are you trying to achieve? If you want to ensure you dont lose everything when a disk dies then your already covered.

    you can add another disk to the server as a "hot spare" which would ensure you have no loss of speed if a drive fails and should cover you if you lose two disks at once.

    If your wanting to increase space, you can just add another disk into the raid 5 array, giving you 640GB of usable space.
    however you must remember that you CANNOT resize the system partition of your server.

    I hope some of this information is useful :\ can you please say what the problem is or what you are trying to achieve then we should be able to see what we can do to help

    Thanks
    -Tony

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    greenfieldsupport's Avatar
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    also, to add...

    The system partition, being part of the RAID 5 array, especially as it holds your Active Directory info, IS A GOOD THING!

    as with the RAID 5 not only do you have the performance boost but you have redundancy and fault tolerance

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    greenfieldsupport's Avatar
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    http://www.nthelp.com/raidlev.htm

    Read this should give you some basic info.

    Mirroring is always an expensive and bad option, I see it does say that RAID 5 is slower but i disagree, I'd count mirroring (raid 1) as alot slower than Raid 5, especially at reading.

    EDIT(
    If you need reliability and to minimise the chance for downtime, you need RAID 6 (which is RAID 5 with two sets of parity instead of the original one), and for even more reliability you can add hot spairs to that aswell.

    IF you need it to be very fast (thx torledo) and you dont care about having to start from scratch with your machine after a disk fault, go for RAID 0.
    )
    e.g. for my home gaming machine

    but for anything that involves work / schools / servers. Stick to your RAID 5
    Last edited by greenfieldsupport; 23rd January 2008 at 05:13 PM.

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    ozydave's Avatar
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    What am I trying to achieve is basically a backup of the windows partition, so if windows becomes corrupt then a I have backup of a working windows partition which I could restore.
    I know I could make a ghost image of the partition but that could be problematic with a hardware raid
    Just looking for an easer solution

  8. #8

    SYNACK's Avatar
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    In that case you are definatly after an imaging or backup method as with mirroring if one windows installation gets corrupted the mirror will have the exact same problem.

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    mattx's Avatar
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    What am I trying to achieve is basically a backup of the windows partition, so if windows becomes corrupt then a I have backup of a working windows partition which I could restore.
    Don't you have any backups in place then ?

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    Quote Originally Posted by ozydave View Post
    What am I trying to achieve is basically a backup of the windows partition, so if windows becomes corrupt then a I have backup of a working windows partition which I could restore.
    I know I could make a ghost image of the partition but that could be problematic with a hardware raid
    Just looking for an easer solution

    mirroring will have both disks the same all the time, so the only thing it does is protect you from hardware failure (even then it ins't fool proof, i've had power surges take out both hdd's)

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    greenfieldsupport's Avatar
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    Right, Well basically mirroring is Deffo's not your solution. If a file was to corrupt then an identical copy of the error + corrupted file would be placed on both the original drive and the copy. The only way mirroring would help is if a drive was to fail, which your covered for as you have hardware RAID 5

    You need a backup solution. And you need something that will let you recover the entire partition should it fail.

    Most people use Symantec Backup Exec.

    We use Symantec Livestate system recovery.

    Essentially they both do the same job of backing up your system partition (and if you want the other partitions) to restore if something goes drastically wrong.

    However just a warning, normally you can recover from most windows errors but if something goes wrong to the point where you have to recover, its usually easier (im going to get shouted at by everyone for saying this) to just take the oppertunity to rebuilt the server.

    Because A. it should be alot faster after a rebuild
    and B. because theres a chance that should your server fail, you could restore to a backup you made a week ago... and in 7 days time the same thing could happen...

    I guess its personal choice, for me the most important thing is the data. If the server goes down then using system recovery software I can either A. restore the server in a few hours or B. host the server as a virtual sever, on the back of another server, to get everything back up and running while i rebuild my server again

    Search around on the forums for easy to use backup software..

    The stuff that comes with windows isnt half bad, but it wont get your server back up and running very fast if something was to go wrong...

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    greenfieldsupport's Avatar
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    lol sorry guys i spent a while writing my reply seems youve answered him already :P

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    SYNACK's Avatar
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    You might want to look at this software ShadowProtect it can take an image of your system every two hours (differential so it only has to store changes) and can restore you back to that point in time.

    Had it recommended by one of our suppliers, never got it though as we had already expended our budget.

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    torledo's Avatar
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    Quote Originally Posted by greenfieldsupport View Post
    http://www.nthelp.com/raidlev.htm

    Read this should give you some basic info.

    Mirroring is always an expensive and bad option, I see it does say that RAID 5 is slower but i disagree, I'd count mirroring (raid 1) as alot slower than Raid 5, especially at reading.

    if you have mission critical and you dont care about having to start from scratch with your machine after a disk fault, go for RAID 0.

    e.g. for my home gaming machine

    but for anything that involves work / schools / servers. Stick to your RAID 5
    Mirroring may be more expensive in that you are utilising only half of you're available raw disk capacity, but it is a perfectly adequate fault-tolerant setup for the system partition of most types of windows server. Most servers just don't need RAID 10 levels of performance on the root/system volume -

    if you have mission critical and you dont care about having to start from scratch with your machine after a disk fault, go for RAID 0.
    Now that's an oxymoron if ever i heard one......mission critical and non-nested, pure, bog standard RAID 0 should not be used in the same sentence....ever.

  15. #15
    greenfieldsupport's Avatar
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    Maybe what i think mission critical is and you do vary.

    I believe mission critical as being VERY VERY DESPERATELY FAST,

    and unless your talking more than 5 disks, theres not faster than RAID 0



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