Re: Mirroring help

From: Phil S. (nospam-m-phil-NoSpam_at_123.net)
Date: 04/06/04 

Date: Tue, 6 Apr 2004 13:33:03 -0400

Vince:

Since no one else has offered help, allow me to offer some background.
(this is a real long post.) This applies to a SBS 4.5 system only.

1st, as I presume from your post you are trying to mirror hard drives from
Windows Disk Manager. Most professional Windows server administrators know
not to use the OS disk mirror since it only uses up precious processor time
and RAM. The better solution is to use SCSI hard drives and to do the RAID
1 or RAID 5 in BIOS which means a high priced expansion I/O card with its
own microprocessor, RAM and firmware. Thus Windows never knows about or has
to deal with the Mirror. It is not uncommon to have 10, or more
physical hard drives in a server.

2nd, Mirroring is not a backup solution. It is just for fault tolerance.
All hard drives use platters that spin on physical bearings. All bearings
are mechanical, and will mechanically fail at some time. Having a mirror or
RAID 5 (striped with checksum), allows the system to remain operational for
a short time with a single hard drive failure. This is just like a
redundant power supply is needed for fault tolerance.

Backups are for restoring files that have been deleted, compromised, or
trashed. Yes, I have several times had a file that was corrupted on a RAID
drive, and all copies are bad. When you write to a mirrored hard drive,
both physical partitions are written to almost immediately. A virus that
attacks a file will have attacked both copies on a mirrored system.

3rd, SBS 4.5 and all things Windows NT 4.0 for that mater, have a 2 GB limit
on the C:\ drive. This is a limit due to DOS file system during the install
of a NT system. If you convert the drive to NTFS file system, you could use
a product like Powerquest's (I think Symantec owns it now) Partitionmagic,
or VolumeMagic and you could extend the size of the C:\ drive to a little
over 8 GB.

3A - Many administrators only mirror the NT C:\ drive so they can boot the
system if a drive fails. However, in high end BIOS RAID solutions, if the
another drive is RAID 5, and you run out of disk space, you can add
another physical hard drive to the array and the SCSI RAID controller will
spread out the array to fit the new physical drive into the expanded
array.

4th, the Concept of mirroring, or RAID 1, is to spread the fault tolerance
across several physical hard drives. Please think about this, while you
could mirror a partition on a hard drive to free space on the same drive,
what you gain in tolerance if that hard drive died? nothing? Less than
nothing I would guess.

5th, having a mirror or RAID solution to fault tolerance is only as good as
the administrator who knows what to do when the fault occurs. If you have a
mirror, and one hard drive fails, you must know how, and have practiced
doing, recovering from the fault. As in break the mirror, boot the system
to be operational, purchase a replacement, when the replacement arrives
install it, and reconfigure the mirror, and allow the system to copy across
the data.

Now, if you have two hard drives with multiple partitions on each disk, and
you want to mirror.
     partition the one of new physical hard drives to match partition by
        partition of the one of the current drives
     partition the other new to match the other current hard drive partition
       by partition.
     Format each of partitions on the new drives to match the format of the
       current drives FAT16, NTFS or whatever.
     Now Mirror partition by partition current to new so you end up with
        two identical hard drives one new and one old.

Now practice breaking the mirror and try to recover for booting and running.
  (pull the power cord on the hard drive with the power off)

HTH ( I have check this several time for accuracy, but be aware, I could
have left something important out. Double check with others)

Phil. S.

"Vince" <anonymous@discussions.microsoft.com> wrote in message
news:ueWEca5GEHA.2392@tk2msftngp13.phx.gbl...
> I Posted this earlier and didn't get any response, even a laugh.
> If I have posted in the wrong place, or insulted someone, please let me
> know.
> Or let me know where I could post to get help on mirroring, I would most
> certainly appreciate it.
> If you looked at my post and can't help, please let me know, so I can
start
> searching elsewhere
> Thanks
> Vince
>
>
> Hi all,
> My first time mirroring and I'm in trouble already!!
> We have SBS4.5 at sp6. The system started with 2 physical drives (4gb
each).
> When I installed the system, I believe there was an option to create
> a system extension on another volume for things like SQL, User software,
> etc..
> I took that option.
> I ended up with about a 2gb vol C:, a 1gb vol E: Sys extension, and 1gb
free
> space on physical unit 0.
> On the other physical unit I created a 2gb vol F: Business, holds our
> business software, and 2gb free space.
> We have decided to mirror everything and purchased and installed 2
identical
> drives.
> Before I mirrored the F: volume I wanted to make the best use of the drive
> space and gave the F: volume the free space on its physical drive.
> This work fine and I ended up with one big volume F: on that drive. I then
> mirrored it to the physical drive I wanted and that work great too. Now
I'm
> thinking, Boy did they make this easy.
> Ha!! Now we come to the system vol C: and E: system extension. Beings the
> system vol. C: gets filled up with log records I decided to give it the
1gb
> of free space on it's physical unit. I was promptly told that I couldn't
do
> this as it is the system volume(I know I read that somewhere).
> I figured I would give the space to the E: sys extension and point the
> logging crap to it. When I tried to do this instead of ending up with one
> vol E: sys extension, like I got with the vol F: I ended up with 2 vol E:
> sys extensions each in their own little boxes in the disk administrator
> window.
> I figured this is ok and tried to mirror what I had. It wouldn't let me
> select all of it an create the mirror, so I selected Vol C: and that
> mirrored. When I selected Vol E: sys extension and clicked fault tolerance
> on the menu "Mirror" was grayed out. I Had committed previous stuff and
> rebooted.
> What am I doing wrong?? Can I copy the stuff in Vol E: sys extension to a
> temp folder on my F: volume, delete the E: sys extension from the physical
> drive, create another E: system extension that uses up all the free space
on
> that drive and then copy the stuff back?? Or will SBS swear at me, and
turn
> my system into a vegetable because I screwed with its paths, pointers,
> permissions and other magical stuff???
> Any Help Would be appreciated
> Vince
>
>

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