How does one know a Mirrored RAID is working?

Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

This sounds stupid and is kinda like trying to figure out if the light
in the fridge goes out when you close the door.

P5AD2-E Premium
SIL3114 SATA RAID controler
2-200 GB Seagate 7200.7 SATA Drives

I connected everything up. The SIL ROM Utility recognized the drives
and I selected a mirror and had the utility automatically setup the
array.

When I went to the Disk Managment in windows XP it ran the new Disk
wizard. Windows only shows 1 disk as I would expect if the controller
is handling the mirror functionality. I setup a new volume and it only
presented the options of simple volume and not RAID Mirror. Windows
shows the disk as Dynamic, 186.31GB NTFS, Healthy.

Question? How does one tell that both drives are getting the data such
that there is backup if one disk fails?
4
answers
Last reply
More about mirrored raid working
  1. Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

    Ususally via a utility included in your mobo disk, and from mobo site.
    ie satalink
    Also on bootup there is an option to enter raid setup screen, the boot up
    screen also gives a msg regarding state of raid.
    Disk Management will only see a single disk, and not a mirror.


    "dwswager" <dwswager@knology.net> wrote in message
    news:1113060297.022817.37660@o13g2000cwo.googlegroups.com...
    > This sounds stupid and is kinda like trying to figure out if the light
    > in the fridge goes out when you close the door.
    >
    > P5AD2-E Premium
    > SIL3114 SATA RAID controler
    > 2-200 GB Seagate 7200.7 SATA Drives
    >
    > I connected everything up. The SIL ROM Utility recognized the drives
    > and I selected a mirror and had the utility automatically setup the
    > array.
    >
    > When I went to the Disk Managment in windows XP it ran the new Disk
    > wizard. Windows only shows 1 disk as I would expect if the controller
    > is handling the mirror functionality. I setup a new volume and it only
    > presented the options of simple volume and not RAID Mirror. Windows
    > shows the disk as Dynamic, 186.31GB NTFS, Healthy.
    >
    > Question? How does one tell that both drives are getting the data such
    > that there is backup if one disk fails?
    >
  2. Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

    dwswager wrote:
    > This sounds stupid and is kinda like trying to figure out if the light
    > in the fridge goes out when you close the door.

    No, actually it's a rally good question.

    > P5AD2-E Premium
    > SIL3114 SATA RAID controler
    > 2-200 GB Seagate 7200.7 SATA Drives
    >
    > I connected everything up. The SIL ROM Utility recognized the drives
    > and I selected a mirror and had the utility automatically setup the
    > array.

    OK.

    > When I went to the Disk Managment in windows XP it ran the new Disk
    > wizard. Windows only shows 1 disk as I would expect if the controller
    > is handling the mirror functionality. I setup a new volume and it only
    > presented the options of simple volume and not RAID Mirror. Windows
    > shows the disk as Dynamic, 186.31GB NTFS, Healthy.

    Right.

    > Question? How does one tell that both drives are getting the data such
    > that there is backup if one disk fails?

    Well it would seem that what you want to do is simulate a drive failure.
    When the drive doesn't have any power, or is not connected to the SATA
    controller, it appears quite dead (unplug a drive). Your Array,
    however, should carry on - hopefully it'll moan at you as well.

    I wonder how many people have religously done backups only to find out
    that none of them worked, because they were doing something wrong? If
    you're going to go to the expense/bother to backup or make your data
    redundant, check that it really is!

    Ben
    --
    A7N8X FAQ: www.ben.pope.name/a7n8x_faq.html
    Questions by email will likely be ignored, please use the newsgroups.
    I'm not just a number. To many, I'm known as a String...
  3. Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

    In article <1113060297.022817.37660@o13g2000cwo.googlegroups.com>,
    "dwswager" <dwswager@knology.net> wrote:

    > This sounds stupid and is kinda like trying to figure out if the light
    > in the fridge goes out when you close the door.
    >
    > P5AD2-E Premium
    > SIL3114 SATA RAID controler
    > 2-200 GB Seagate 7200.7 SATA Drives
    >
    > I connected everything up. The SIL ROM Utility recognized the drives
    > and I selected a mirror and had the utility automatically setup the
    > array.
    >
    > When I went to the Disk Managment in windows XP it ran the new Disk
    > wizard. Windows only shows 1 disk as I would expect if the controller
    > is handling the mirror functionality. I setup a new volume and it only
    > presented the options of simple volume and not RAID Mirror. Windows
    > shows the disk as Dynamic, 186.31GB NTFS, Healthy.
    >
    > Question? How does one tell that both drives are getting the data such
    > that there is backup if one disk fails?

    I think this is an excellent question. Someone posted a problem
    to this group once, where a disk in their mirror failed, and
    the data on the remaining drive was missing data/out of date.
    I can only presume that the status shown in Windows all that t
    ime was "healthy", when in fact it was not.

    The mirror state is based on a premise. The premise is that,
    exactly the same operation is done to each disk. If the RAID
    hardware and software detect a diverge of this assumption, then
    the status of the array should immediately change, to reflect
    that the assumption is no longer true.

    This means, when the motherboard POSTs, both disks must answer
    queries in the first 30 seconds or so. If a disk fails to
    respond, the RAID BIOS/software must mark the remaining disk
    as an orphan, and tell the user the array is broken.

    Similarly, if the mirror is doing a write operation, and one
    disk fails to complete the write operation, that should result
    in the array being broken.

    Corner cases can occur, if the computer is not powered by a
    UPS. If the power is cut to the computer, when one disk has
    succeeded in writing its sector, and the second disk has not,
    there is no way to record the divergence of the two disks.
    What happens then, might very well depend on whether the
    file system is journalled or not. In any case, the disks could
    diverge from that point onwards.

    A similar situation could occur, if the RAID chip you are using
    is a "soft RAID". For example, I have read that the SIL0680 is
    a soft RAID. The thing is, if the RAID driver crashes, and has
    only written data to one disk, that is the same thing as the
    power failed case. I would at least want a solution where the
    "mirroring" is done purely by hardware.

    If a RAID chip is truly "hardware", the RAID chip will make
    sure that both disks get written, or it will present a status
    that there is a failure. If the software driver to the hardware
    chip fails, if will fail "atomically", as either a single command
    is given to the hardware chip to write both disks, or the
    single command has not been given.

    There is, I suppose, the possibility that a bus crash (arbiter
    failure) could freeze out the RAID hardware chip, before it can
    complete identical operations on both drives.

    In summary, I think you can see there are many possibilities
    for the array to become desynchronized. Perhaps taking the
    array offline once in a while, and checksumming all the files
    on the disk would help. For this to work, you would have to
    find an IDE or SATA interface, that is not going to be
    confused by the presence of the "reserved sector" on the disk.

    If you are using the Promise 20378, for example, you could
    flip the BIOS setting from "RAID" to "IDE", connect one
    drive, and create a manifest for the disk. (A manifest is
    a directory listing, plus a checksum for each file.) Repeat
    for the other disk. Run a chkdsk (NOT repair option) on
    each disk, to see if any files are damaged from an abrupt
    termination before a file was completely written, or a
    directory structure was updated.

    Based on the results of the test, you could choose to return
    to RAID land, reenable RAID operation, break the array, and
    re-clone one disk to the other. Because you have done chkdsk,
    a surface scan, a manifest, you would be reasonably sure that
    the cloning operation will succeed.

    Which is a hell of a lot of work, and explains why I for one
    am not interested in a mirror, when I can have a backup image
    taken once in a while instead. If mirroring software was capable
    of doing a consistency check on both volumes of a mirror,
    perhaps my opinion would change. As long as the only automated
    option is to re-clone one disk to the other, you'll never
    know whether hidden faults are collecting on one of the disks.
    And tearing the array down, to checksum it, is not going to be
    a "free' operation, if the user has to do it.

    Paul
  4. Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

    I posted the problem with missing data on a mirror.
    All utilities, and post, showed mirror in sync. ie no problems.
    Asus acknowledged a problem with Sil controller and apparently an early
    bios.
    I am moving to a dedicated Raid card/controler
    Yes I had full offsite and onsite backups, which is why I lost nothing.
    At least when the hd failed, my mirror drive was up and running in some 1
    min.

    "Paul" <nospam@needed.com> wrote in message
    news:nospam-0904052338290001@192.168.1.178...
    > In article <1113060297.022817.37660@o13g2000cwo.googlegroups.com>,
    > "dwswager" <dwswager@knology.net> wrote:
    >
    > > This sounds stupid and is kinda like trying to figure out if the light
    > > in the fridge goes out when you close the door.
    > >
    > > P5AD2-E Premium
    > > SIL3114 SATA RAID controler
    > > 2-200 GB Seagate 7200.7 SATA Drives
    > >
    > > I connected everything up. The SIL ROM Utility recognized the drives
    > > and I selected a mirror and had the utility automatically setup the
    > > array.
    > >
    > > When I went to the Disk Managment in windows XP it ran the new Disk
    > > wizard. Windows only shows 1 disk as I would expect if the controller
    > > is handling the mirror functionality. I setup a new volume and it only
    > > presented the options of simple volume and not RAID Mirror. Windows
    > > shows the disk as Dynamic, 186.31GB NTFS, Healthy.
    > >
    > > Question? How does one tell that both drives are getting the data such
    > > that there is backup if one disk fails?
    >
    > I think this is an excellent question. Someone posted a problem
    > to this group once, where a disk in their mirror failed, and
    > the data on the remaining drive was missing data/out of date.
    > I can only presume that the status shown in Windows all that t
    > ime was "healthy", when in fact it was not.
    >
    > The mirror state is based on a premise. The premise is that,
    > exactly the same operation is done to each disk. If the RAID
    > hardware and software detect a diverge of this assumption, then
    > the status of the array should immediately change, to reflect
    > that the assumption is no longer true.
    >
    > This means, when the motherboard POSTs, both disks must answer
    > queries in the first 30 seconds or so. If a disk fails to
    > respond, the RAID BIOS/software must mark the remaining disk
    > as an orphan, and tell the user the array is broken.
    >
    > Similarly, if the mirror is doing a write operation, and one
    > disk fails to complete the write operation, that should result
    > in the array being broken.
    >
    > Corner cases can occur, if the computer is not powered by a
    > UPS. If the power is cut to the computer, when one disk has
    > succeeded in writing its sector, and the second disk has not,
    > there is no way to record the divergence of the two disks.
    > What happens then, might very well depend on whether the
    > file system is journalled or not. In any case, the disks could
    > diverge from that point onwards.
    >
    > A similar situation could occur, if the RAID chip you are using
    > is a "soft RAID". For example, I have read that the SIL0680 is
    > a soft RAID. The thing is, if the RAID driver crashes, and has
    > only written data to one disk, that is the same thing as the
    > power failed case. I would at least want a solution where the
    > "mirroring" is done purely by hardware.
    >
    > If a RAID chip is truly "hardware", the RAID chip will make
    > sure that both disks get written, or it will present a status
    > that there is a failure. If the software driver to the hardware
    > chip fails, if will fail "atomically", as either a single command
    > is given to the hardware chip to write both disks, or the
    > single command has not been given.
    >
    > There is, I suppose, the possibility that a bus crash (arbiter
    > failure) could freeze out the RAID hardware chip, before it can
    > complete identical operations on both drives.
    >
    > In summary, I think you can see there are many possibilities
    > for the array to become desynchronized. Perhaps taking the
    > array offline once in a while, and checksumming all the files
    > on the disk would help. For this to work, you would have to
    > find an IDE or SATA interface, that is not going to be
    > confused by the presence of the "reserved sector" on the disk.
    >
    > If you are using the Promise 20378, for example, you could
    > flip the BIOS setting from "RAID" to "IDE", connect one
    > drive, and create a manifest for the disk. (A manifest is
    > a directory listing, plus a checksum for each file.) Repeat
    > for the other disk. Run a chkdsk (NOT repair option) on
    > each disk, to see if any files are damaged from an abrupt
    > termination before a file was completely written, or a
    > directory structure was updated.
    >
    > Based on the results of the test, you could choose to return
    > to RAID land, reenable RAID operation, break the array, and
    > re-clone one disk to the other. Because you have done chkdsk,
    > a surface scan, a manifest, you would be reasonably sure that
    > the cloning operation will succeed.
    >
    > Which is a hell of a lot of work, and explains why I for one
    > am not interested in a mirror, when I can have a backup image
    > taken once in a while instead. If mirroring software was capable
    > of doing a consistency check on both volumes of a mirror,
    > perhaps my opinion would change. As long as the only automated
    > option is to re-clone one disk to the other, you'll never
    > know whether hidden faults are collecting on one of the disks.
    > And tearing the array down, to checksum it, is not going to be
    > a "free' operation, if the user has to do it.
    >
    > Paul
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