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"Kevin O'Gorman" 12-02-2011 01:56 AM

Getting started the hard way with RAID
 
I'm in the late stages of recovering a broken system. The original
had a hardware raid controller managing a mirror set that contained
some stuff that was not backed up. Fortunately, one reason it wasn't
backed up is that it wasn't really vital. Nevertheless, I'd like to
get at that stuff.

The hard part is that I no longer have that RAID controller, just the
two drives. The controller was a 64-bit PCI card, and the new mobo
cannot handle it. The mirror set does not show up at all in fdisk or
gparted, though it's pretty obvious where it is. Early in the
recovery process, some other piece of software told me it saw the
mirror set, but I don't remember which software that was.

I left the drives uncabled since then. Now I have them online again
and I don't know where to start. They seem healthy, and still have
the two non-RAID partitions they're supposed to have.

Is it possible for LVM to see that data?
Any idea what tools I would need to finish the recovery? Or am I just SOL?


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Ioannis Vranos 12-02-2011 02:24 AM

Getting started the hard way with RAID
 
On Fri, Dec 2, 2011 at 4:56 AM, Kevin O'Gorman <kogorman@gmail.com> wrote:
> I'm in the late stages of recovering a broken system. *The original
> had a hardware raid controller managing a mirror set that contained
> some stuff that was not backed up. *Fortunately, one reason it wasn't
> backed up is that it wasn't really vital. *Nevertheless, I'd like to
> get at that stuff.
>
> The hard part is that I no longer have that RAID controller, just the
> two drives. *The controller was a 64-bit PCI card, and the new mobo
> cannot handle it. *The mirror set does not show up at all in fdisk or
> gparted, though it's pretty obvious where it is. *Early in the
> recovery process, some other piece of software told me it saw the
> mirror set, but I don't remember which software that was.
>
> I left the drives uncabled since then. *Now I have them online again
> and I don't know where to start. *They seem healthy, and still have
> the two non-RAID partitions they're supposed to have.
>
> Is it possible for LVM to see that data?
> Any idea what tools I would need to finish the recovery? *Or am I just SOL?


I do not think LVM can see your RAID 1. As far as I know, LVM is like
RAID 0, with the exception that it writes on the second HDD after the
first one fills.

However Linux supports Software RAID 1. You may have a look at dmraid,
or mdadm tools.


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Ioannis Vranos 12-02-2011 02:28 AM

Getting started the hard way with RAID
 
On Fri, Dec 2, 2011 at 5:24 AM, Ioannis Vranos <ioannis.vranos@gmail.com> wrote:
>
> I do not think LVM can see your RAID 1. As far as I know, LVM is like
> RAID 0, with the exception that it writes on the second HDD after the
> first one fills.
>
> However Linux supports Software RAID 1. You may have a look at dmraid,
> or mdadm tools.


I think this can be useful regarding mdadm tool:
https://help.ubuntu.com/community/Installation/SoftwareRAID#Using_mdadm


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Marius Gedminas 12-02-2011 08:30 AM

Getting started the hard way with RAID
 
On Thu, Dec 01, 2011 at 06:56:30PM -0800, Kevin O'Gorman wrote:
> I'm in the late stages of recovering a broken system. The original
> had a hardware raid controller managing a mirror set that contained
> some stuff that was not backed up. Fortunately, one reason it wasn't
> backed up is that it wasn't really vital. Nevertheless, I'd like to
> get at that stuff.
>
> The hard part is that I no longer have that RAID controller, just the
> two drives. The controller was a 64-bit PCI card, and the new mobo
> cannot handle it.

Have you googled for the model and manufacturer of that RAID controller?

AFAIU most hw RAID solutions have their own custom data/metadata formats.
Chances are you can't access the data easily without a working hardware
RAID controller of the same manufacturer, but perhaps you're in luck,
and your particular metadata format is supported by dmraid.

I'm not familiar with dmraid, unfortunately, but I've glanced at the
manual page online, and it seems to support some kind of autodiscovery.
Have you tried it?

Marius Gedminas
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"Kevin O'Gorman" 12-02-2011 04:44 PM

Getting started the hard way with RAID
 
On Fri, Dec 2, 2011 at 1:30 AM, Marius Gedminas <marius@pov.lt> wrote:
> On Thu, Dec 01, 2011 at 06:56:30PM -0800, Kevin O'Gorman wrote:
>> I'm in the late stages of recovering a broken system. *The original
>> had a hardware raid controller managing a mirror set that contained
>> some stuff that was not backed up. Fortunately, one reason it wasn't
>> backed up is that it wasn't really vital. *Nevertheless, I'd like to
>> get at that stuff.
>>
>> The hard part is that I no longer have that RAID controller, just the
>> two drives. *The controller was a 64-bit PCI card, and the new mobo
>> cannot handle it.
>
> Have you googled for the model and manufacturer of that RAID controller?

Not yet, but I will. It was a 3ware 9550SX controller.

> AFAIU most hw RAID solutions have their own custom data/metadata formats.
> Chances are you can't access the data easily without a working hardware
> RAID controller of the same manufacturer, but perhaps you're in luck,
> and your particular metadata format is supported by dmraid.
>
> I'm not familiar with dmraid, unfortunately, but I've glanced at the
> manual page online, and it seems to support some kind of autodiscovery.
> Have you tried it?

I have not really tried much of anything, but I will. Up to now I've
been too busy getting the urgent stuff back online. Well, urgent as
hobbies go anyway.

Plus I've been reluctant to fool with things that might harm the data.

The controller was my first experiment with RAID, and I've decided it
was a bad fit to my situation. As a hobbyist, I don't have spare
drives to drop in when one goes down, I don't have a spare motherboard
to support the controller, or a spare controller, when things go
south. Not having used this stuff before, it hadn't occurred to me to
worry if the on-disk format was proprietary, but now I see the
problem.

I'm probably not going to implement software RAID either, except to
the extent it might make it easier to get at the old RAID stuff. I've
worked out a nice set of scripts to do backups to "external" drives in
external drive docks, and I have six 2TB sata drives dedicated to
archival storage. This even supports off-site storage.

> Marius Gedminas

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"compdoc" 12-02-2011 05:13 PM

Getting started the hard way with RAID
 
>Not yet, but I will. It was a 3ware 9550SX controller.

I use the 3ware 9650se family of controls, and they’ve been great at allowing me to move the drives from one controller to another. Maybe another controller from the 9550SX family would give you similar results.

I use the controllers for raid5 arrays of sata drives.




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"Kevin O'Gorman" 12-03-2011 04:21 AM

Getting started the hard way with RAID
 
On Fri, Dec 2, 2011 at 10:13 AM, compdoc <compdoc@hotrodpc.com> wrote:
>>Not yet, but I will. *It was a 3ware 9550SX controller.
>
> I use the 3ware 9650se family of controls, and they’ve been great at allowing me to move the drives from one controller to another. Maybe another controller from the 9550SX family would give you similar results.
>
> I use the controllers for raid5 arrays of sata drives.

It might help, but I don't want to buy one. I have no obvious way to
borrow one.

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"Kevin O'Gorman" 12-03-2011 04:35 AM

Getting started the hard way with RAID
 
On Fri, Dec 2, 2011 at 10:13 AM, compdoc <compdoc@hotrodpc.com> wrote:
>>Not yet, but I will. *It was a 3ware 9550SX controller.
>
> I use the 3ware 9650se family of controls, and they’ve been great at allowing me to move the drives from one controller to another. Maybe another controller from the 9550SX family would give you similar results.
>
> I use the controllers for raid5 arrays of sata drives.

Are your 9650se controllers for PCI-e? They might be what I need now.
The old one was PCI-X.


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Avi Greenbury 12-03-2011 11:39 AM

Getting started the hard way with RAID
 
Kevin O'Gorman wrote:
> >> The hard part is that I no longer have that RAID controller, just
> >> the two drives. *The controller was a 64-bit PCI card, and the new
> >> mobo cannot handle it.
> >
> > Have you googled for the model and manufacturer of that RAID
> > controller?
>
> Not yet, but I will. It was a 3ware 9550SX controller.

Generally, you will need a new, working, raid card of at least the same
family, sometimes the same model, to get the data off the disks. This
is the huge disadvantage to hardware (or even fake) raid, and why
generally I'd just stick with software raid unless I can have another
raid card on standby. Dmraid's worth a look; I've never had cause to
try it.

> The controller was my first experiment with RAID, and I've decided it
> was a bad fit to my situation. As a hobbyist, I don't have spare
> drives to drop in when one goes down, I don't have a spare motherboard
> to support the controller, or a spare controller, when things go
> south. Not having used this stuff before, it hadn't occurred to me to
> worry if the on-disk format was proprietary, but now I see the
> problem.

Well, you only need raid if you need high-availability. In the vast
majority of cases, the additional disk in a raid pair can be put to
better use as a backup.

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David Fletcher 12-03-2011 12:36 PM

Getting started the hard way with RAID
 
On Sat, 2011-12-03 at 12:39 +0000, Avi Greenbury wrote:
> Kevin O'Gorman wrote:

> Generally, you will need a new, working, raid card of at least the same
> family, sometimes the same model, to get the data off the disks. This
> is the huge disadvantage to hardware (or even fake) raid, and why
> generally I'd just stick with software raid unless I can have another
> raid card on standby. Dmraid's worth a look; I've never had cause to
> try it.
>
> Well, you only need raid if you need high-availability. In the vast
> majority of cases, the additional disk in a raid pair can be put to
> better use as a backup.
>
> --
> Avi
>

I was wondering about using RAID myself, when I built my home server a
few years back. I talked about it with the other guys at the LUG. For my
application, the points against it were something like:-

1) Adding extra hard drives means I have more electricity to pay for

2) The more parts you put into a box, the quicker something will fail

3) If it's a hardware RAID board that goes wrong, you're screwed unless
you can get another, compatible one

4) It adds complexity to the system.



So, I've got just a single, 1TB Samsung EcoGreen I think it's called,
hard drive that's now been running 24/7 for about 18 months now. Apart
from the couple of power cuts that were long enough to empty the UPS
battery.

What I believe to be true of hard drives is that they're a little bit
like car engines in that the worst thing you can do to them is keep
switching them on and off. The so-called fluid dynamic bearings that
they now all use are apparently pretty similar to the big end bearings
in an engine in that they run on an oil film and if operating as
intended, avoid all metal-metal contact. Not that that's the only thing
that can go wrong, with all the included electronics.

So, now that my drive has been running long enough to obviously not be
an infant death candidate, and is kept at a pretty comfortable
temperature, and if the long MTBF numbers claimed for hard drives these
days are to be believed, it should last for a good few years.

IMHO I'd never run a RAID myself, but in a data centre with loads of
identical servers where any failed hard drives need to be hot swappable,
and presumably a stock of spare hardware is maintained, I guess it is
worthwhile.

Dave



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