"Bob Rafuse" said:
I have P4P800 that I have successfully migrated from a standalone IDE
to an IDE RAID 1 configuration (see earlier thread). Everything is
working fine, but I have a question:
How can I tell if/when one of the drives in the IDE RAID 1 goes bad
and needs replacing? Do I need to run the VIA RAID Tool at startup?
Will that tell me? Or does the VIA XP driver write an event to the XP
event log?
Any pointers, suggestions and/or dope-slaps anyone can provide would
be greatly appreciated.
Bob
The first warning you will get, is in the BIOS. The BIOS
should have RAID code, and when that code is loaded at
POST, it checks the connected drives, for the special
reserved sector containing RAID ID info. If it finds
one drive of a mirrored pair, but cannot find the other,
it should be marking the array as "busted".
The BIOS should stop at that point.
For example, you may get the occasional nuisance error
report from the RAID BIOS, say if one of the drives in
the mirror is not detected within the timeout period.
In a case like that, I think people repair the problem
by deleting the array and creating the array again.
Creating the array, should copy the data from the drive
that was first detected, to the drive that was late
starting up. A good RAID controller will allow the rebuild
to occur, while the array is being used.
The RAID BIOS or OS software, is going to try to do
things such that the drives continue to be exact mirrors.
The info stored in the reserved sector should be
maintained by those softwares, to keep track of what
state the array is currently in. (And failure of the
reserved sector, is a possible failure mechanism for
the drive. Say if there is a power failure while the
heads of the disks are positioned over the reserved
sector. Sometimes the only thing missing in a failure
event, is the reserved sector.)
You should be offered the option to boot with just
one drive of the mirrored set available. Once booted,
any RAID tools provided for use with the OS can be used.
You may be able to build the array while the system is
running, and return to a proper mirrored pair again.
The time to test how a RAID mirror works, is before you
have the data on it. Create a mirror, then disconnect
both drives, format one of the drives (on an ordinary
IDE interface somewhere) to simulate a problem, connect
the drives to the RAID controller, and practice repairing
the problem. You don't want to be learning how to do
maintenance on the drive, when your life's work is stored
on there, you have no backup, and you cannot figure out
which drive is which. (Placing sticky labels on the drives
would be a good idea.)
For those reasons, I would rather have a good backup on
a removable device, than have a mirror. I like to have
a single drive on a computer, to get the best theoretical
reliability numbers possible, without going to the
complexity of using a mirror or RAID5. Operator error
represents a significant danger to your reliability numbers,
so knowing how to use the RAID array is important.
Having a RAID does not eliminate the need for backups. You
could have a power supply failure, say the +12V goes too
high, and burns out the motors on all disk drives at the
same time. Or say a lightning strike takes out the computer.
A backup on a removable piece of media would be invaluable
in a situation like that, whether you have a mirror or not.
You might also purchase a UPS, the kind that will allow an
orderly shutdown if you are away from the computer. The
array can be desynchronized if the power goes off in the
middle of a write operation, and I doubt the array will
detect it. (The data on the two disks would diverge, and
the drives might not be exact mirrors any more.) For that
reason, it is a good idea to equip a RAID computer with a UPS.
What the mirror could buy you, is better "uptime", say if
you are doing professional Photoshop work on the machine,
and a disk goes out on you in the middle of the day. You
could continue to run with just the one disk, until your
current project is finished. Maybe that is worth something.
For other more casual uses of the computer, I'd prefer the
symplicity of using a single drive, plus frequent incremental
and total backups. A failure is a more abrupt event, but
with your spare blank drive in hand, and last night's
backup, you can be back up in a couple of hours.
(Also, on the topic of backups. In my years of watching other
people using computers, I've seen multiple occurrences of
people who were taking backup snapshots, without ever testing
that the restore function works. Typically, a tape drive that
never gets cleaned, is involved. The shocked looks on their
faces is priceless, when they discover their backup software
doesn't do restores properly, or none of the tapes in the
current rotation, has any data on it.)
Paul
