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 the data on the remaining drive was missing data/out of date.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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