[Novalug] SATA HD with LVM on RAID/ udev needed?

[Brandon Saxe]

Thanks for the response! Very helpful advice. I have some follow-up questions in-line. Please keep in mind this will be my first Linux Soft-RAID experience.

Thanks again,
  Brandon


--- On Sun, 6/29/08, RJ Bergeron <rbergero at gmail.com> wrote:

> From: RJ Bergeron <rbergero at gmail.com>
> Subject: Re: [Novalug] SATA HD with LVM on RAID/ udev needed?
> To: brandon20va at yahoo.com
> Cc: "novalug mailing list" <novalug at calypso.tux.org>
> Date: Sunday, June 29, 2008, 7:46 PM
> On Sun, Jun 29, 2008 at 19:26, Brandon Saxe
> <brandon20va at yahoo.com> wrote:
> > ?- My SATA controller is a Silicon Image and hot swap
> is supported. Is there any special thing I need to do to
> let the kernel know when I am about to remove/insert a
> drive (of course after unmounting any filesystem first). Is
> it okay to just 'umount' and unplug? Does
> 'eject' matter here or maybe there's some SCSI
> commands I should issue? I am not sure.
> I've not played with the eject code, I heard it is
> working these days
> for SATA, but don't have anything I'm willing to
> try it with.
> According to http://linux-ata.org/software-status.html
> (Search for
> 'hotplug supprt'), you just yank it... I'm not
> sure how the SATA
> backplane deals with this, if at all.
> 
> > ?- Device Names. Depending on the order the drives are
> inserted/removed, the device name changes from anything
> between /dev/sdd to /dev/sdf. I have also seen /dev/sdg on
> testing. For reference, I have two other SATA drives
> attached to mobo at /dev/sda and /dev/sdb. /dev/sdc is a
> USB drive. Do I need to configure udev rules for each drive
> in order for my system to function correctly? OR will RAID
> and LVM figure all that out for me?
> Linux's MD software writes a signature to each disk and
> uses that to
> figure out how to assemble the RAID. This lets you do very
> silly
> things like swap out PATA controllers for a stack of
> USB->PATA
> boxes...

Are you suggesting to always use RAID or LVM even if for just one disk? I guess one example may be a USB external hard drive. By having LVM manage the disk, then LVM daemon will know exactly where to mount it every time without caring for the /dev node name? 

> 
> > ?- Should I bother dealing with udev on this one? Even
> if RAID and LVM don't care about device names, I still
> feel it may be helpful to know exactly which drive is at
> which device node. Can anybody recommend why I *should* or
> *shouldn't* do udev?
> I would stay away from configuring udev to map drives
> statically, it's
> just not necessary and may confuse the MD assembly
> processes ('seeing'
> things twice). I actually recently replaced a failed drive
> (through
> coldplug, ATA100 here...) by noticing the actual failed
> device in
> /proc/mdstat, then running smartctl -a /dev/hde (my device)
> so I knew
> which model/serial number I needed to pull.

Are you saying you run RAID with even one disk to be able to use software RAID monitoring tools? 

> 
> RJ