Questions[fdisk](server)

We have a large ~18TB hardware raid array on a Dell R720xd. Currently the RAID5 array consists of 6x4TB and I needed to extend it.

Step 1 expand the hardware raid array.

Simple enough if you have the dell admin tools installed.

omconfig storage vdisk action=reconfigure controller=0 vdisk=1 raid=r5 pdisk=0:1:0,0:1:1,0:1:3,0:1:3,0:1:4,0:1:5,0:1:8,0:1:9

( new disks were the last two, which can be confirmed by using the omreport tool) That all went fine though it takes a while, and I was able to confirm the array had been expanded..

% omreport storage vdisk controller=0 vdisk=1

Virtual Disk 1 on Controller PERC H710P Mini (Embedded)

Controller PERC H710P Mini (Embedded)
ID                                : 1
Status                            : Ok
Name                              : bak
State                             : Ready
Hot Spare Policy violated         : Not Assigned
Encrypted                         : No
Layout                            : RAID-5
Size                              : 26,078.50 GB (28001576157184 bytes)
...
Device Name                       : /dev/sdb
...

Step 2 new partition

So the vdisk is now reporting the increased ( 26TB ) size. and fdisk does concur...

Disk /dev/sdb: 25.5 TiB, 28001576157184 bytes, 54690578432 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: A2D20632-37D1-4607-9AA0-B0ED6E457F91

Device     Start         End     Sectors  Size Type
/dev/sdb1   2048 39064698846 39064696799 18.2T Linux LVM

However when I go to add an additional partition to the disk the following happens...

Command (m for help): n
Partition number (2-128, default 2): 2
First sector (34-2047): 

I now have about 16 Billion more sectors on the disk, but I can't use them. I am only offered Sectors 34-2047. I cannot allocate the 8TB of new space even though I am currently setup with just a single partition.

The other thing that did strike me as odd was the fact that I was offered partition numbers 2-128, not simply 2-4. The partition table doesn't show any extended partition so I would have expected that to limit me to just 4 partitions initially.

Is there anything I am missing?

• The machine has been rebooted since the drive array was expanded. Before that fdisk would report only the original 18TB
• Trying cfdisk instead just reports 2015 sectors available in the 39 Billion range despite reporting 25TB overall.
• We don't want to delete and re-create the partition if we can avoid it, given we could loose all the data. We are preferring to simply extend the LVM volume group with the new partition once done.
• Its a similar issue to Another server Fault question, but I am not limited by having run out of partitions, and I don't think I'm being restricted by an extended partition.
• Its not sector size being expanded by the drive expansion. If it were fdisk would not be reporting the sector count increase I would have thought. Plus pvs and vgs are not reporting any additional un-allocated space under LVM
• I ran this as a dry run on a virtual machine and did not experience this. However I was shutting down the vm and increasing its disk device size. So it was not online during the size increase. Plus the drive sizes were many orders of magnitude smaller for the vm.

Update 1 'x'pert mode output requested by Micheal...

Command (m for help): x

Expert command (m for help): p
Disk /dev/sdb: 25.5 TiB, 28001576157184 bytes, 54690578432 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: A2D20632-37D1-4607-9AA0-B0ED6E457F91
First LBA: 34
Last LBA: 39064698846
Alternative LBA: 39064698879
Partitions entries LBA: 2
Allocated partition entries: 128

Device     Start         End     Sectors Type-UUID                            UUID                                 Name      Attrs
/dev/sdb1   2048 39064698846 39064696799 E6D6D379-F507-44C2-A23C-238F2A3DF928 E9CB58BF-F170-4480-A230-6E2A238367D1 Linux LVM 


Expert command (m for help): v
MyLBA mismatch with real position at backup header.
1 error detected.

So a possible LBA error?

doing a fdisk -l is a quite convenient command, but how to make fidsk print the partition size in a unit such as MB or GB?

This is disgusting to me, but it works:

echo -e "n\np\n1\n\n\nt\nc\na\n1\nw" | fdisk /dev/sdb

I would like to know a more prudent or elegant way to accomplish this. The entire boot record and partition table is being zeroed prior to this task, so we can trust that partition 1 is available.

How do you delete all partitions on a device from the command line on Linux (specifically Ubuntu)? I tried looking at fdisk, but it presents an interactive prompt. I'm looking for a single command, which I can give a device path (e.g. /dev/sda) and it'll delete the ext4, linux-swap, and whatever other partitions it finds. Essentially, this would be the same thing as if I were to open GParted, and manually select and delete all partitions. This seems fairly simple, but unfortunately, I haven't been able to find anything through Google.

Sometimes, when resizing or otherwise mucking about with partitions on a disk, cfdisk will say:

Wrote partition table, but re-read table failed. Reboot to update table.

(This also happens with other partitioning tools, so I'm thinking this is a Linux issue rather than a cfdisk issue.) Why is this, and why does it only happens sometimes, and what can I do to avoid it?

Note: Please assume that none of the partitions I am actually editing are opened, mounted or otherwise in use.

Update:

cfdisk uses ioctl(fd, BLKRRPART, NULL) to tell Linux to reread the partition table. Two of the other tools recommended so far (hdparm -z DEVICE, sfdisk -R DEVICE) does exactly the same thing. The partprobe DEVICE command, on the other hand, seems to use a new ioctl called BLKPG, which might be better; I don't know. (It also falls back on BLKRRPART if BLKPG fails.)

BLKPG seems to be a "this partition has changed; here is the new size" operation, and it looked like partprobe called it individually on all the partitions on the device passed, so it should work if the individual partitions are unused. However, I have not had the opportunity to try it.