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Thread: Raid 1

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    Raid 1

    New computer, and my first Raid 1 configuration (my first RAID for that matter). An HP desktop Pavilion with Vista. I understand that the D drive mirrors the C drive exactly, and that if the C crashes I still have the D. Can someone tell me and/or refer me the the best sources so that I can understand the followiing: 1. How will I know when C goes down? 2. How will I know if D goes down? 3. What do I then do: does the other drive just function automatically? Does it give me a message as to what has happened? 4. How do I get the system back to the Raid 1 configuration after the corrupted drive is removed and replaced? 5. etc.What are some other things I should know?

    Thanks

    kdoc

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    Re: Raid 1

    I think you are asking exactly the right questions. Many people think that RAID will "just work" and don't plan for how they will recover when a disk fails - this often results in disappointment.

    My usual advice would be to forget the RAID, and use the second drive to store regular backups, have a look at the comments I made in <post:=593,536>post 593,536</post:>.

    If you insist on using RAID to protect this disk then you will need to find information specific to the particular disk controller to get answers to your questions. There are no generic answers. Recovery from a failed disk is probably available from the BIOS level, but if you don't practice then you may accidentally copy the data the wrong way when you replace the failed drive! Can you let us know exactly what model of PC and Disk Controller you have, so we can look it up.

    StuartR

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    Re: Raid 1

    Thanks Stuart: It's late, and I haven't yet read your previous post. I have an HP Pavilion, D4790Y, with 2 250 SATA HDDs in Raid 1 configuration. and an Intel ® 82801HR/HH/HO SATA Raid Controller, and Microsoft iSCSI Initiator. Under disk drives it only shows "Raid 1." Also here's something puzzling: I went into Device Manager to get the information you requested, and under Processors, it shows two Intel® Core (tm)2CPU 6600 @ 2.40GHz. As far as I know I only have one. Is this just the way a core 2 duo processor shows up? Or do I have a quad core by mistake?

    I, too, am inclined to think I should have just gotten Raid 0 or just 2 drives. Which of the two do you prefer. And...were I to switch, just how easy is that--to go to Raid 0 or to just two drives? I should say I'm current in NO MOOD (after installing this computer and my crashed Dell laptop harddrive) to start from scratch and reformat, etc.

    By the way: I started asking HP tech support this and other questions, and they're totally useless. The tech guy had the gall to suggest I look in Google [img]/forums/images/smilies/smile.gif[/img].

    kdoc

    kdoc

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    Re: Raid 1

    A quick browse of the HP web site shows that you configure the RAID using software that runs under Windows XP, but I couldn't find any detail of the user interface.

    I would think it must be fairly simple to convert this from RAID 1 to two separate drives, but if the documentation and software don't make this obvious, why not go to the HP web site and log a support call to find out how.

    Your second question about the number of CPUs. If you have a CPU that supports HyperThreading then it will appear to Windows as two CPUs, since it can schedule two threads to run at the "same" time.

    StuartR

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    Re: Raid 1

    I'm not sure I agree with what you are saying!

    In RAID 1 you have two drives which mirror each other. Whatever is on one drive should be at all times exactly the same as on the other. So if your drive is set up with just a C: partition, the exact same exists on the second drive. If you have C:, D:, and E: partitions on one drive, you have the same on the other. Windows tends to ignore the fact that you have (hardware) RAID 1, which you can verify by looking at Disk Manager, and leaves it up to the RAID controller card to manage the disk accessing.

    I have a Promise RAID controller in my PC, with a pair of RAID 1/mirrored (nominal) 400 GB drives. See that Disk Manager only shows me as having the one drive. (Drive D: is not assigned (unless I put a USB Flash Drive into a USB socket), drive E: is my External Maxtor backup drive, and my DVD-ROM and DVD-RW drives are R: (read-only) and Wwriteable), in case you're puzzled!).

    If one drive of the mirror fails, then you should just be able to carry on running with the other drive until such time as you are able to replace it with (preferably) an identical model, and the RAID controller software will rebuild the RAID mirror at startup (it may take a staggering amount of time, mind you!).

    There are rare circumstances where a missing Master Boot Record is duplicated on both drives, thus rendering the mirroring rather futile, and that is the reason I ended up with twin 400-GB drives instead of the original twin-160 GB drives (a long story...).

    John

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    Re: Raid 1

    Thanks: ...whatever hyperthreading is [img]/forums/images/smilies/smile.gif[/img]. I've called tech support 4 times so far, and they're totally,completely, awfully useless!!. I'll try again.

    kdoc

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    Re: Raid 1

    Where do you see the drives (you mention "Disk Manager")? The way they've configured this, I can see drive C in Windows Explorer (it says 149 GB free of 226 GB, and then it shows "Recovery (D, and then says 902 MB free of 6.83 GB. If I double click it, it does open with the various files. There's several files showing in it, but not identical to C. There's a SystemRecovery.txt in it which simply says "Vista System Recovery Partition."

    kdoc

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    Re: Raid 1

    Looks to me that you have the usual HP 'recovery partition' visible as D:, and the operating system partition as C: (surprise!). You will have these on BOTH physical drives, such that if you broke the mirror and disconnected either drive you would still be able to boot from the connected drive's C: partition. Unfortunately my HP desktop just has the one hard drive, so I can't show you.

    You should observe "Disk Management" highlighted to the left of the screen dump...

    The hyperthreading matter is a red-herring - just accept that your single CPU seems to work as two halves. In practice it is somewhat more efficient, but you don't really see any effect from this!

    John

    PS Dells usually have a recovery partition too, but this is (somewhat) hidden and does not get assigned a drive letter.
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    Re: Raid 1

    Thanks John: It looks like we're getting somewhere, and I understand you can'dt be too specific, as you don't have this. But would you please go back to my original question and see whether you can answer the various parts. On my side, I'll try tech support when I have another hour to waist. What exactly is "the usual HP recovery padrtition?"

    kdoc

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    Re: Raid 1

    > What exactly is "the usual HP recovery padrtition?"

    HP Notebook PCs - Using the PC Recovery Solution

    StuartR

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    Re: Raid 1

    I thought some/most of your questions had already been answered by Stuart or me, but I'll have a bash at them again:

    Can someone tell me and/or refer me the the best sources so that I can understand the followiing:
    1. How will I know when C goes down?
    2. How will I know if D goes down?
    3. What do I then do: does the other drive just function automatically? Does it give me a message as to what has happened?


    As I said before, you should not be talking about the C: partition and the D: partition, but disk 1 and disk 2 of the RAID-1 mirrored set. Each holds an exact copy of the two partitions, C: and D:, maintained like this by the RAID controller card. The RAID controller software/drivers will tell you pretty rapidly if it detects it can't read or write to one of the drives. It isn't always obvious, though, to which drive the messages refer, so be careful. (Often the usual problem about whether the drive count starts at 0 or at 1...). There will be a way to get into the configuration just after boot time, so it may be worth you pressing Ctrl+A (or whatever the key sequence is) and get familiar with the layout of RAID information well before you need to...

    4. How do I get the system back to the Raid 1 configuration after the corrupted drive is removed and replaced?

    The RAID software automatically rebuilds the mirror/RAID set on a restart, when it detects that the failed drive (whichever it should be) has been replaced. This is pretty early on in the boot process, to make things simpler for itself. It will probably format the new drive before writing the data from the working drive to it, so don't hold your breath.

    5. etc.What are some other things I should know?

    Err... Among other comments:
    Mirroring does not give you protection against an error (unspecified type!) on one drive being propagated to the second drive.
    You MUST have a standard form of backup of the [files/operating system/system state/registry/you name it] separate from the RAID set. (Perhaps Acronis TrueImage or Ghost or the like?)
    Treat the RAID-1 mirror as just an additional (and different) form of data security, but do NOT rely on it as being foolproof.

    John
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    Re: Raid 1

    Thank you very much John: Yes, I suppose you two did answer much of this, and that I just didn't read it as carefully as I might have. This whole subject is alien to me and I may have missed some of the subtleties. It seems like there's no problem. I'll just ask one more thing (I think). In the interest of getting a lock on the drive count/configuration ahead of time, where exactly do you mean? As I mentioned, Windows Explorer calls them C and D drive, and Acronis just refers to Disk 1. Devise Manager simply lists them under "Disk Drives" as "Raid 1." When exactly do I press the key sequence you suggest? Is it on normal boot up?

    Anyway thanks to both of you. You've got to love this forum!! [img]/forums/images/smilies/smile.gif[/img].

    keith

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    Re: Raid 1

    Let me have a go at trying to explain the relationship between C: D: and your two physical drives.

    Assume that each of your two disk drives is 300GB (it doesn't matter if this is wrong, it's just to illustrate the point).

    The disk controller will call these disk 0 and disk 1, and it will make sure that every single block on Disk 1 is identical to the corresponding block on Disk 0.
    The disk controller will tell Windows that it just has one disk, with room for 300GB of data, so in Disk Manager you will only see a single disk drive. Even though there are two identical disk drives, these aren't visible to any software except the driver for the disk controller. Everything else sees a single 300GB drive.

    When the disk partitions were created, windows thought that it was creating two partitions, C: and D:, on the one disk that it knows about. The disk controller actually made two copies of everything, but windows can just see one disk with two partitions. All of the data for C: is on both disks, all of the data for D: is also on both disks.

    StuartR
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    Re: Raid 1

    Hi folks: While I feel that this issue has been pretty clearly explained and settled, I thought I'd post what the HP tech support said tonight--finally having called me back from my previous calls. This is to the best of my note-taking ability! It pretty well "mirrors" (pun intended) what you (plural) have said.

    There are 2

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