Mailinglist Archive: opensuse (2348 mails)

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Re: [opensuse] Software IDE RAID versus hardware IDE RAID
  • From: "David C. Rankin" <drankinatty@xxxxxxxxxxxxxxxxxx>
  • Date: Wed, 02 Apr 2008 23:00:27 -0500
  • Message-id: <47F4565B.7030005@xxxxxxxxxxxxxxxxxx>
Sandy Drobic wrote:

On modern systems the cpu load is no longer an argument, even if you were to use software RAID5. The real argument is ease of use:
software raid cannot include /boot, so you have to provide redundancy for /boot in some other way.


Hmmm. Sandy,

I don't know if that is true anymore. The last 3 software raid systems I set up, using Yast, everything except swap was included in the raid array. That included / /boot and /home. I agree that you are only using one disk to "boot" from with grub using:

title openSUSE 10.3 - 2.6.23.17-ccj64
root (hd0,4)

However, hd0 is mapped to the raid array where:

[22:40 nirvana/boot] # cat grub/device.map
(hd0) /dev/mapper/nvidia_hacfgfda

So I am booting from the 5th partition (or the pc slice number in the BSD terminology) where "4" the partition is counted from "0". hd0 is the software raid array built from /dev/sda and /dev/sdb in raid1:

22:28 nirvana~> sudo dmraid -r
/dev/sda: nvidia, "nvidia_hacfgfda", mirror, ok, 976773166 sectors, data@ 0
/dev/sdb: nvidia, "nvidia_hacfgfda", mirror, ok, 976773166 sectors, data@ 0

with partitions:

22:18 nirvana~> cat /etc/fstab
/dev/mapper/nvidia_hacfgfda_part7 / ext3 acl,user_xattr 1 1
/dev/mapper/nvidia_hacfgfda_part5 /boot ext3 acl,user_xattr 1 2
/dev/mapper/nvidia_hacfgfda_part8 /home ext3 acl,user_xattr 1 2
/dev/mapper/nvidia_hacfgfda_part6 swap swap defaults 0 0

So in my case, the system is booting off from (hd0,4) or the 5th partition on the raid array with is /boot which is mirrored between /dev/sda and /dev/sdb.

I don't know whether grub has internal logic to select an individual disk to boot from, but I believe that the physical disk boot selection is governed by the BIOS selection of hard disk boot priority.

So it appears that /boot is mirrored and also used to boot as well.


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David C. Rankin, J.D., P.E.
Rankin Law Firm, PLLC
510 Ochiltree Street
Nacogdoches, Texas 75961
Telephone: (936) 715-9333
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www.rankinlawfirm.com
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