[Discuss] raid controller drivers

[joe at polcari.com (Joe Polcari)]

Yes lvm and sw raid are in initrd. I always sw mirror /boot on a 2-300 MB and never had a problem using the mirror for recovery. 

Sent from my android device.

-----Original Message-----
From: John Hall <johnhall2.0 at gmail.com>
To: Joe Polcari <Joe at polcari.com>
Cc: Boston Linux and Unix <discuss at blu.org>
Sent: Thu, 25 Sep 2014 2:30 AM
Subject: Re: [Discuss] raid controller drivers

I agree with Richard that it's easier to put grub and kernels on a non-raid
disk. You can also use that disk to save details of the configuration. If
you want speed consider an ssd for boot. It only uses a slice of the drive,
and you'd avoid all these problems with initrd  - and also perhaps grub as
well.   I had a system set up to boot from a software raid array but now
I'm much happier booting that system from SSD. I also save some
configuration data useful for recovery on the ssd.

I think there may be a script someplace to convert all disk settings to use
UUIDs.

I believe that some hardware raid cards are configured on system boot with
a settings interface you could enter with a correctly timed key stroke like
bios settings. ... Of course much has changed with boot over the last
several years. At least with some controllers, the disks are available
separately, but the single joined disk is not available until you have
entered the setup and configured the disks as a raid volume.  You could
also just use mdraid to create the array from the disks, which will be
about the same if the raid controller is a firmware controller without a
dedicated processor and cache.

I seem to remember that another gotcha is that grub might need to read from
the controller if the boot volume is on the array. Grub can read from
mdraid and lvm but at one point you had to set those modules to load, or be
dropped to a prompt and load them yourself. Maybe it's now default,
detected,... configured when you install the os.. I'm not sure... and don't
know if you'd run into the same issue with hardware raid if you can
configure the controller to present the array as a single sas or sata disk.

One downside of raid is that whenever you read or write anything all the
disks spin up. That generates more heat than reading from a single disk. I
had two disc logic boards die at the same time because a fan on the
backplane failed.   I was using raid5 and so had to recover one of the
discs and replace the second one. I was able to replace the logic board but
it had to be a board from a very close serial number match... model match
was not good enough. Ugh! I finally got the array back up... I used the
lowest $/gb sata disks I could find. Good for you for using SAS disks !
Even so If you leave this system running you might want to monitor the disk
temperature.


On Wed, Sep 24, 2014 at 2:22 PM, Joe Polcari <Joe at polcari.com> wrote:

> I can't give you the exact steps off the top of my head, too dependent on
> google lately, but all you have to do once the correct driver is loaded is
> add the module to your initrd. On RH you can mkinitrd or you can actually
> do
> the process manually.
>
> -----Original Message-----
> From: discuss-bounces+joe=polcari.com at blu.org
> [mailto:discuss-bounces+joe=polcari.com at blu.org] On Behalf Of Stephen
> Adler
> Sent: Wednesday, September 24, 2014 1:58 PM
> To: Richard Pieri
> Cc: discuss at blu.org
> Subject: Re: [Discuss] raid controller drivers
>
> On Wed, 2014-09-24 at 13:54 -0400, Richard Pieri wrote:
> > On 9/24/2014 1:23 PM, Stephen Adler wrote:
> > > OK... so my question is, how do I configure the boot image to force it
> > > to include the SAS raid controller driver so I can boot from a disk
> > > connected to it?
> >
> > If it were me, you don't. I avoid doing this because it's a pain in the
> > ass thanks to the Linux kernel's broken device enumeration mechanism.
> > Instead, boot from a vanilla SATA disk on a vanilla SATA port set to be
> > the first BIOS boot device. Optionally, mirror the boot volume with
> > mdadm and set the two devices as first and second BIOS boot devices.
> >
>
> Thanks Richard, that's how my system is setup right now. I was hoping to
> get rid of the generic SATA setup to boot fedora 20 and have a full SAS
> system booting from the SAS controller. So be it...
>
> Cheers. Steve.
>
>
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