Mailinglist Archive: opensuse (963 mails)

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Re: [opensuse] create md RAID1 from old HD's ordinary partition with data plus new virgin HD's empty 0xFD partition
On 4/20/2011 4:00 AM, Per Jessen wrote:
Felix Miata wrote:

On 2011/04/20 09:21 (GMT+0200) Per Jessen composed:

Felix Miata wrote:

Before adding sda14 to md7 with mdadm, does anyone have any
comments or advice that might prevent needing to restore sdb14's
content from backup?


Pong - like I tried to hint four days ago, I think you ought to
investigate how the --build option really works and how you create
persistent superblocks.

Your previous reply coupled to this reply constitutes about an equal
number or words to what the mdadm man page has to say about build,
which is to say little better than useless. The man page ends with
these words: "the Build mode should only be used together with a
complete understanding of what you are doing". Investigate how and

Google, the linux-raid mailing list and perhaps even the source code.
Unfortunately it doesn't look like the --build option is used very

Why should any ordinary user trying to replace a disk with the
only kind available, bigger, even care what a persistent superblock

A user that is confident enough to use mdadm --build ought to know what
a persistent superblock is. I'm not sure "ordinary" is quite the right
word here.

No ordinary user should need to understand any more than how to use
YaST2 and/or mdadm to couple an old partition to a new blank space on
a replacement disk to create another raid1 device. It seems just too
basic& common a job to do.

I think it's neither basic nor very common to want to create a new RAID
device based on data on an existing non-RAID drive. Just my opinion of

My _guess_ is that you can go ahead and add sda14 to md7 without
problems, but without a persistent superblock, it can't be used for
booting from.

I was going to say "what happened when you tried it?" As in, why not just try some experiments with small ramdisks? You can create virtual block devices, and mdadm them into arrays, slice, dice, fail, rebuild, remove, re-add, etc all you like without ever touching a real disk or rebooting or anything. Just be sure to use all clearly distinguisable names for the temp ramdisks and arrays that can't be mistaken for any of your real devices so with all the normally dangerous commands you'll be using so many times in such a short while you aren't at unnecessary risk of zapping any real disks or filesystems.

Then you will know for sure what a given command will do before you have to do it on the real disks. Iv'e done some weird repairs on software raid arrays and I don't think I've ever used --build either so I can't simply say what exactly it does or whether you want it or something else either.

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