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Old 12-15-2012, 09:45 AM   #1
sewerurchin
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Copying partition table to new disk


Hi,

I'm trying to get a disk ready for use in a new RAID 1 array. Here are the steps that I am following:

- Dump partition table from existing disk into file:
sfdisk -d /dev/sdd > sdd.out

- cat sdd.out
# partition table of /dev/sdd
unit: sectors

/dev/sdd1 : start= 63, size= 1959867, Id=fd, bootable
/dev/sdd2 : start= 1959930, size= 7807590, Id=fd
/dev/sdd3 : start= 9767520, size= 59936160, Id=fd
/dev/sdd4 : start= 69703680, size=418691375, Id=fd

- Load partition table def into new disk
sfdisk /dev/sde < sdd.out

That works OK. The thing I don't understand is this:
Why does /dev/sde1 have a filesystem on it? There are no filesystems on sde3 or sde4. Shouldn't running 'sfdisk /dev/sde < sdd.out' wipe out all of the filesystems on /dev/sde? TIA for your help.

Model: ATA ST3250823AS (scsi)
Disk /dev/sdd: 250GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number Start End Size Type File system Flags
1 32.3kB 1003MB 1003MB primary ext2 boot, raid
2 1003MB 5001MB 3997MB primary linux-swap(v1) raid
3 5001MB 35.7GB 30.7GB primary ext4 raid
4 35.7GB 250GB 214GB primary ext4 raid

Model: ATA ST3250823AS (scsi)
Disk /dev/sde: 250GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number Start End Size Type File system Flags
1 32.3kB 1003MB 1003MB primary ext2 boot, raid
2 1003MB 5001MB 3997MB primary linux-swap(v1) raid
3 5001MB 35.7GB 30.7GB primary raid
4 35.7GB 250GB 214GB primary raid
 
Old 12-15-2012, 05:24 PM   #2
syg00
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Quote:
Originally Posted by sewerurchin View Post
Shouldn't running 'sfdisk /dev/sde < sdd.out' wipe out all of the filesystems on /dev/sde?
Nope, it merely updates the partition table, which contains the start and size of each of 4 primary partitions in your case. Nothing is touched outside of the MBR (again, in your case).
Most first partitions start at the same sector, so if a filesystem existed there previously, and is no larger than the newly defined partition, it will be valid. Then same is also possible for later partition(s), but they must align exactly to the correct sector on the disk. Much less likely.
 
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Old 12-15-2012, 05:59 PM   #3
sewerurchin
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Ok, thanks. So what do I do if I want to remove the filesystem?
 
Old 12-15-2012, 06:03 PM   #4
syg00
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Code:
dd if=/dev/zero of=/dev/sde1 count=100
Should do it.
Watch for typos (mine as well as your own) ...
 
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Old 12-15-2012, 06:17 PM   #5
sewerurchin
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That's pretty much what I figured, but I was a little afraid of 'experimenting' and messing something up.
 
  


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