On-disk format of fakeraid raid1

[bigby]

Hi all

I have knowledge of Linux but not much in Windows.

I would like to set up a home server with RAID-1 (2 disks) in Windows,
including boot, hence I need to leverage the fakeraid in the mainboard
(mainboard which I still have to buy) (*)

All will be nice except if/when the mainboard breaks.

So I would really like if someone could tell me that in case of failure
I will be able to replace the broken mainboard with a different
mainboard with a different controller, and that the new controller will
be able to at least read one of the two disks of the array like if it
was a single non-raid disk.

For this to happen, the metadata of fakeraid raid1 needs to be at the
end of the disk. Otherwise finding the partitions (skipping the metadata
at the beginning) would require a difficult and uncertain low-level
hacking and then MBR fixing.

So do you know if this is the case for usual fakeraids?

AND THEN:

After successfully booting with 1 disk only, I would like to be able to
even recreate the raid1 on the (different) fakeraid controller of the
second mainboard.

For this to be possible I need the fakeraid to allow me create the raid1
while keeping the data of at least one of the two disks. I.e. if the
first operation of raid-1 creation is filling the two disks with zeroes,
I am doomed.

So is this standard, for what you have seen?

Also in order to be able to port raid1's to another fakeraid, I guess I
need to leave enough space after the last partition so to accommodate
every possible fakeraid raid1 metadata. This is because if the first
mainboard's fakeraid takes only 4K for metadata but the second mainboard
takes 100MB, and my last partition touches the end of the disk after the
first raid1 creation, during the creation of the raid1 on the second
mainboard the first 99.99MB of the metadata would overwrite my last
partition.

So do you have an idea of how much space should I leave free at the end?


(*) or do you know if Windows (any version) allows software raid-1
starting from boot-time? I don't think so huh? If yes, please can you
point me to a web tutorial/information?


Thank you in advance

 

[Arno]

Hi all

I have knowledge of Linux but not much in Windows.

I would like to set up a home server with RAID-1 (2 disks) in Windows,
including boot, hence I need to leverage the fakeraid in the mainboard
(mainboard which I still have to buy) (*)

All will be nice except if/when the mainboard breaks.

So I would really like if someone could tell me that in case of failure
I will be able to replace the broken mainboard with a different
mainboard with a different controller, and that the new controller will
be able to at least read one of the two disks of the array like if it
was a single non-raid disk.

That cpuld be problematic. But if you have Linux competence,
you can do something else: If the fake-raid is supported by
dm-raid (Linux Fakeraid driver), you can make a sector image
of the array to a third disk (or to the second one as
the new fakeraid with a different dm-raid setting if you are
daring). I really would recommend using a third disk, so you
still have a backup after adding the second disk to the new
raid.

For this to happen, the metadata of fakeraid raid1 needs to be at the
end of the disk. Otherwise finding the partitions (skipping the metadata
at the beginning) would require a difficult and uncertain low-level
hacking and then MBR fixing.

So do you know if this is the case for usual fakeraids?

Usuallu not, because they are intentionally incompatible,
vendor lock-in and all that business "optimization".

AND THEN:

After successfully booting with 1 disk only, I would like to be able to
even recreate the raid1 on the (different) fakeraid controller of the
second mainboard.

For this to be possible I need the fakeraid to allow me create the raid1
while keeping the data of at least one of the two disks. I.e. if the
first operation of raid-1 creation is filling the two disks with zeroes,
I am doomed.

So is this standard, for what you have seen?

No. As I said, vendors try to intentionally make this hard
or impossible.

Also in order to be able to port raid1's to another fakeraid, I guess I
need to leave enough space after the last partition so to accommodate
every possible fakeraid raid1 metadata. This is because if the first
mainboard's fakeraid takes only 4K for metadata but the second mainboard
takes 100MB, and my last partition touches the end of the disk after the
first raid1 creation, during the creation of the raid1 on the second
mainboard the first 99.99MB of the metadata would overwrite my last
partition.

So do you have an idea of how much space should I leave free at the end?

Not a lot. Leave 1GB off to be really, really safe.

(*) or do you know if Windows (any version) allows software raid-1
starting from boot-time? I don't think so huh? If yes, please can you
point me to a web tutorial/information?

I think windows has this "dynamic disk" concept in the professional
versions, but I have no experience with it and do not know whether
you can reliably boot from it with one disk gone or at all.

I think you should investigate dm-raid and in case the thing breaks
image over with it. Image-copies of windows typically work, at
least I have never had problems imaging my c:\ with linux
or restoring it.

I do not know whether dm-raid has a webpage, but
google(dmraid) gives you a lot og info. Also the
source is here

http://people.redhat.com/~heinzm/sw/dmraid/src/

and probably contains embedded documentation.

Arno

 

[Bob Willard]

Hi all

I have knowledge of Linux but not much in Windows.

I would like to set up a home server with RAID-1 (2 disks) in Windows,
including boot, hence I need to leverage the fakeraid in the mainboard
(mainboard which I still have to buy) (*)

All will be nice except if/when the mainboard breaks.

So I would really like if someone could tell me that in case of failure
I will be able to replace the broken mainboard with a different
mainboard with a different controller, and that the new controller will
be able to at least read one of the two disks of the array like if it
was a single non-raid disk.

For this to happen, the metadata of fakeraid raid1 needs to be at the
end of the disk. Otherwise finding the partitions (skipping the metadata
at the beginning) would require a difficult and uncertain low-level
hacking and then MBR fixing.

So do you know if this is the case for usual fakeraids?

AND THEN:

After successfully booting with 1 disk only, I would like to be able to
even recreate the raid1 on the (different) fakeraid controller of the
second mainboard.

For this to be possible I need the fakeraid to allow me create the raid1
while keeping the data of at least one of the two disks. I.e. if the
first operation of raid-1 creation is filling the two disks with zeroes,
I am doomed.

So is this standard, for what you have seen?

Also in order to be able to port raid1's to another fakeraid, I guess I
need to leave enough space after the last partition so to accommodate
every possible fakeraid raid1 metadata. This is because if the first
mainboard's fakeraid takes only 4K for metadata but the second mainboard
takes 100MB, and my last partition touches the end of the disk after the
first raid1 creation, during the creation of the raid1 on the second
mainboard the first 99.99MB of the metadata would overwrite my last
partition.

So do you have an idea of how much space should I leave free at the end?


(*) or do you know if Windows (any version) allows software raid-1
starting from boot-time? I don't think so huh? If yes, please can you
point me to a web tutorial/information?


Thank you in advance

Bad thinking. You need a comprehensive backup procedure (meaning a
program plus some practices) to cover all of the events that could
corrupt all HDs in a RAIDset. And, with good backups, a failed MB
would need no more than MB replacement followed by restoring the
content of the RAIDset. (And, if the new MB is different from the
old MB, a repair/install of Windows will probably be needed; simple,
if you have a valid disk for the OS.)

Backups will also work if you decide to replace the HDs in your
RAIDset, to increase capacity or speed; or if you decide to
upgrade the MB or CPU or RAM or OS or ...

RAID is not a replacement for backup. Period.

 

[bigby]

bigby wrote:
Backups will also work if you decide to replace the HDs in your
RAIDset, to increase capacity or speed; or if you decide to
upgrade the MB or CPU or RAM or OS or ...

RAID is not a replacement for backup. Period.

RAID is a replacement for RAID!

I have never asked a backup. You read wrong.

I already have a backup for data but that takes lots of time for
restoring if the OS is gone. So I also wanted the RAID.

Do you know a type of backup that will reinstall all installed applications?

 

[Bob Willard]

RAID is a replacement for RAID!

I have never asked a backup. You read wrong.

I already have a backup for data but that takes lots of time for
restoring if the OS is gone. So I also wanted the RAID.

Do you know a type of backup that will reinstall all installed
applications?

If you restore from an image-mode backup of the set of all of
the HDs it should result in all apps being correctly installed.
You may need to do a repair/install of Windows, but all of the
info created during the installation of apps was part of the
image-mode backup; mostly in the registry, which is just a
couple of files. An installed app is, in fact a set of files
and a set of links to those files; those links are stored in
either the registry (files) or in .INI (or equivalent) files.

RAID1 gives you some protection against the failure of a
single HD. It gives you *no* protection against the failure
of any other component in a computer, and many of those
components are more failure-prone than HDs. Furthermore,
RAID1 gives you no protection against transient faults, which
are not failures, but which may cause file corruption; RAID1
gives you no protection against environmental problems (e.g.,
brownouts and lightning strikes) which may cause file
corruption; RAID1 gives you no protection against malware or
badly-designed software which may cause file corruption; and
RAID1 gives you no protection against the most common cause
of lost or corrupted files: fumble-fingers.

Again, RAID1 only gives you some protection against failures
of the most reliable components in a computer. Nice to have,
if you have already covered all of the less reliable stuff.

 

[bigby]

If you restore from an image-mode backup of the set of all of
the HDs it should result in all apps being correctly installed.
You may need to do a repair/install of Windows, but all of the
info created during the installation of apps was part of the
image-mode backup; mostly in the registry, which is just a
couple of files. An installed app is, in fact a set of files
and a set of links to those files; those links are stored in
either the registry (files) or in .INI (or equivalent) files.

Thanks for the info but the hassle of restoring from backups after the
last image was taken is just not worth it. OR the bandwidth needed for
daily backups of the whole HD or partition is just not worth it. That's
why I want RAID1...

RAID1 gives you some protection against the failure of a
single HD. It gives you *no* protection against the failure
of any other component in a computer, and many of those
components are more failure-prone than HDs. Furthermore,
RAID1 gives you no protection against transient faults, which
are not failures, but which may cause file corruption; RAID1
gives you no protection against environmental problems (e.g.,
brownouts and lightning strikes) which may cause file
corruption; RAID1 gives you no protection against malware or
badly-designed software which may cause file corruption; and
RAID1 gives you no protection against the most common cause
of lost or corrupted files: fumble-fingers.

Lots of people on this NG giving lessons on what RAID is, which I know
perfectly...

Again, RAID1 only gives you some protection against failures
of the most reliable components in a computer. Nice to have,

THE MOST RELIABLE COMPONENTS IN A COMPUTER???
C'mon

It's clearly the least reliable one. (Maybe the mainboard could have
similar un-reliabilty).
And it's where important stuff is.

 

[bigby]

I've seen a fair number of computers over the years - perhaps a couple
of hundred. I can only think of one occasion when I saw a true hard
disk failure in a computer that wasn't a worn-out dinosaur or badly
abused in some way, and that failed within a week of use.

Not my experience. I saw 2 disks fail within the last month. Another in
december, another in november.

In my
experience, power supplies and fans

Fans don't bring down the computer immediately. Use Nanoxia or Noctua
for silence & 10 years life.
Power supplies failing, seen only once in my life.

....

Incidentally, since you have knowledge of Linux but not Windows, and are
setting up a server, why are you considering Windows at all? Why not
use Linux with mdadm raid? (And good backup, of course - Linux may be
orders of magnitude better than Windows at keeping your data reliably,
but it's still not perfect.)

Right... problem is some apps are windows-specific and also I am not the
final user for this computer.

I am thinking of virtualization windows inside linux (w/ linux software
RAID), I know KVM but I am not proficient in passing an USB port to the
windows guest for the printer yet (linux drivers for the printer are
problematic) especially I don't know what will happen if disconnected
then reconnected or if computer reboots. Also we have win 2000 pro
licenses which don't support remote desktop, and vnc is not extremely
friendly.

Thank you

 

[bigby]

I have no real experience with KVM either - I have used Virtual Box on
desktops, and OpenVZ on servers (but that's only for Linux guests on a
Linux host).

In fact maybe VirtualBox would be better in this case

As for vnc, I find it friendly enough - I have used it for years for
working with Windows machines over networks (and occasionally Linux
machines, but generally I can do what I need there with ssh). I
recommend TightVNC with the Mirage drivers - I gather version 2 of
TightVNC has a fair number of useful new features.

Thanks for telling, looks interesting.
But there is no 2.0 viewer for linux huh? This is what I need before
being able to use version 2...
At their website it does not even say it is planned :-/ I hope it IS planned