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Re: How do I tell if my partition is aligned for a 64k/RAID-6?

To: "Josef 'Jeff' Sipek" <jeffpc@xxxxxxxxxxxxxx>
Subject: Re: How do I tell if my partition is aligned for a 64k/RAID-6?
From: Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx>
Date: Sat, 27 Dec 2008 09:05:23 -0500 (EST)
Cc: Michal Soltys <soltys@xxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20081227135822.GI6284@xxxxxxxxxxxxxx>
References: <alpine.DEB.1.10.0812250821360.31386@xxxxxxxxxxxxxxxx> <495410F4.5010508@xxxxxxxx> <alpine.DEB.1.10.0812251846270.32331@xxxxxxxxxxxxxxxx> <20081227133824.GH6284@xxxxxxxxxxxxxx> <alpine.DEB.1.10.0812270850490.15403@xxxxxxxxxxxxxxxx> <20081227135822.GI6284@xxxxxxxxxxxxxx>
User-agent: Alpine 1.10 (DEB 962 2008-03-14)


On Sat, 27 Dec 2008, Josef 'Jeff' Sipek wrote:

On Sat, Dec 27, 2008 at 08:53:21AM -0500, Justin Piszcz wrote:
Why bother partitioning?  I also run a Linux SW RAID1 on the host, as you
know the drive letters can change when working on a server.

Example: Before I created the array (RAID-6), my disks were /dev/sda,
/dev/sdb and /dev/sdc (spare), the RAID-6 was /dev/sdd.  After reboot,
/dev/sdd became /dev/sda and /dev/sd[a-c] became /dev/sd[b-d].

In lilo.conf I had:
raid-extra-boot="/dev/sda,/dev/sdb"

If I ran LILO and forgot to fix the lilo.conf to reflect the new drive
mappings:
raid-extra-boot="/dev/sdb,/dev/sdc"

I could be at risk of ruining the partition?

Hrm...interesting point. LILO could mess up the superblock in sector 0.

I try to avoid such situations when possible, to be safe.

:)

I don't know how LILO would handle it, but I would try to use
/dev/disk/by-*/* instead of the rather unstable /dev/sd* names.

Just my 0.02 cents.

Jeff.

Excellent idea.

# lilo
Added 2.6.27.9-1
Added 2.6.27.10-1
Added 2.6.27.10-2 *
The boot record of  /dev/md1  has been updated.
The boot record of  /dev/disk/by-id/scsi-SATA_WDC_WD1500ADFS-_WD-SN#######  has 
been updated.
Warning: /dev/disk/by-id/scsi-SATA_WDC_WD1500ADFD-_WD-SN######## is not on the 
first disk
The boot record of  /dev/disk/by-id/scsi-SATA_WDC_WD1500ADFD-_WD-SN########  
has been updated.

Thanks!

Justin.

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