Re: [gentoo-user] RAID: new drive on aac raid

[Rich Freeman]

On Mon, Oct 5, 2020 at 10:38 AM <karl@××××××××.se> wrote:
>
> Stefan G. Weichinger:
> > On an older server the customer replaced a SAS drive.
> >
> > I see it as /dev/sg11, but not yes as /dev/sdX, it is not visible in "lsblk"
>
> Perhaps theese links will help:
>  https://www.cyberciti.biz/faq/linux-checking-sas-sata-disks-behind-adaptec-raid-controllers/
>  http://updates.aslab.com/doc/disk-controller/aacraid_guide.pdf
>  https://hwraid.le-vert.net/wiki/Adaptec
>

I don't know the details of any of these controllers, but you have the
gist of it.  The RAID controller is abstracting the individual drives
and so the OS doesn't see them.  You need to do at least some of the
configuration through the controller.  That usually requires
vendor-specific software, which is often available for linux, and
which in some cases is packaged for Gentoo.

There are a lot of ways to do something like this.  If you're doing
hardware RAID you'd just replace/etc the disk in the raid (I'm
actually surprised in this case that just swapping the drive in the
same slot didn't already do this), and the hardware RAID will rebuild
it, and the OS doesn't see anything at all.  You might need the
utility, but that is about it.

If you're doing software RAID or just individual disks, then you're
probably going to go into the controller and basically configure that
disk as standalone, or as a 1-disk "RAID".  That will make it appear
to the OS, and then you can do whatever you want with it at the OS
level (stick a filesystem on it, put it in a RAID/lvm, whatever).

I find this sort of thing really annoying.  I prefer HBAs that just do
IT mode or equivalent - acting as a dumb HBA and passing all the
drives through to the OS.  It isn't that it doesn't work - it is just
that you're now married to that HBA card vendor and if anything
happens to the card you have to replace it with something compatible
and reconfigure it using their software/etc, or else all your data is
unreadable.  Even if you have backups it isn't something you want to
just have to deal with if you're talking about a lot of data.

-- 
Rich