Formatting Large Volumes in OpenStack
- UKY CCS RCD
See the article https://ukyrcd.atlassian.net/wiki/x/2RcpBw for how to create a basic OpenStack volume.
A volume larger than 2 TB requires a special method for it to be usable. Like any volume, a large one requires the creation of a "filesystem". The difference with a large volume is that it also requires the use of a program called "parted". This program is meant to help create a special structure for the volume called a GPT partition table.
Log in to the VM (e.g. via SSH) that you have attached the volume to from a previous step. We suggest that you practice the steps below in a fresh VM that you can throw away, one with no important data in case you make a mistake and end up erasing existing data. It's very easy to accidentally do this when doing operations on storage.
You need to have super user (sudo) access to run the disk commands below. Note that the steps below may truncate some of the output. And the output will differ from what you are working on, so look for some similaritiesFirst, run fdis
First, a basic VM has been created that runs CentOS 7 with m1.medium flavor (which comes with 40 GB of disk space). Running `lsblk` ("list block devices") will show the disk present. At this point, no volumes have been attached. vda is the block device that was created at VM launch, a 40 GB disk space accessible by this VM.
$ sudo lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT vda 253:0 0 40G 0 disk └─vda1 253:1 0 40G 0 part /
Outside of this tutorial, I created a 2TB volume and attached it to the VM (either through the web GUI or CLI), lsblk shows the new volume labeled as device 'vdb'. This label may differ in your VM.
$ sudo lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT vda 253:0 0 40G 0 disk └─vda1 253:1 0 40G 0 part / vdb 253:16 0 2T 0 disk
Mounting it will cause an error due to non-existent filesystem on vdb.
$ sudo mount /dev/vdb /mnt mount: /dev/vdb is write-protected, mounting read-only mount: unknown filesystem type '(null)'
We'll use fdisk to format the block device. Passing -l just shows the disks in more detail.
$ sudo fdisk -l Disk /dev/vda: 42.9 GB, 42949672960 bytes, 83886080 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 Disk label type: dos Disk identifier: 0x000b3c5c Device Boot Start End Blocks Id System /dev/vda1 * 2048 83886046 41941999+ 83 Linux Disk /dev/vdb: 2147.5 GB, 2147483648000 bytes, 4194304000 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
Now run fdisk on the new block device (vdb for this example–make sure that you know which disk you're running fdisk on. You'll erase an existing disk if you pick the wrong one). This command tells us that we need to format the device with a GPT partition table.
$ sudo fdisk /dev/vdb Welcome to fdisk (util-linux 2.23.2). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Device does not contain a recognized partition table Building a new DOS disklabel with disk identifier 0xb8c926f8. Command (m for help): $ sudo fdisk /dev/vdb Welcome to fdisk (util-linux 2.31.1). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Device does not contain a recognized partition table. The size of this disk is 9.5 TiB (10468982784000 bytes). DOS partition table format cannot be used on drives for volumes larger than 2199023255040 bytes for 512-byte sectors. Use GUID partition table format (GPT).
- Run the program "parted". It will take you to a shell prompt where you can enter commands within the program.
$ sudo parted /dev/vdb GNU Parted 3.1 Using /dev/vdb Welcome to GNU Parted! Type 'help' to view a list of commands. (parted)
- Type "print" within parted to show current setup, then enter `mklabel`.
(parted) print Error: /dev/vdb: unrecognised disk label Model: Virtio Block Device (virtblk) Disk /dev/vdb: 2147GB Sector size (logical/physical): 512B/512B Partition Table: unknown Disk Flags:
If the previous command shows a warning like:
Warning: The existing disk label on /dev/vdb will be destroyed and all dat a on this disk will be lost. Do you want to continue?
You can input "yes" after you're sure that you're formatting the empty volume (this warning comes up sometimes if you run fdisk and the program automatically creates a different partition table that we don't want.
- Use 'parted' to create a partition for the volume that will have a GPT. Below, see the value for Partition Table. It must show 'gpt' to confirm that the previous command worked.
(parted) mklabel gpt (parted) print Model: Virtio Block Device (virtblk) Disk /dev/vdb: 2147GB Sector size (logical/physical): 512B/512B Partition Table: gpt Disk Flags: Number Start End Size File system Name Flags - Note that the previous step shows no information under the "Number Start End ...". Now we need to tell the program to create the table with a specified size. The size you can get from the "Disk /dev/vdb: 2147GB" line in the previous step. We run `mkpart primary 0GB 2147GB` below. For your own volume, run the command with the size number that your disk is associated with. Again, run print to confirm.
(parted) mkpart primary 0GB 2147GB (parted) print Model: Virtio Block Device (virtblk) Disk /dev/vdb: 2147GB Sector size (logical/physical): 512B/512B Partition Table: gpt Disk Flags: Number Start End Size File system Name Flags 1 1049kB 2147GB 2147GB primary
- Type quit (the result was already saved). You can run parted again and print to confirm that your previous steps were done (check the value for Partition Table, and check the start/end/size values).
(parted) quit Information: You may need to update /etc/fstab. $ sudo parted /dev/vdb GNU Parted 3.1 Using /dev/vdb Welcome to GNU Parted! Type 'help' to view a list of commands. (parted) print Model: Virtio Block Device (virtblk) Disk /dev/vdb: 2147GB Sector size (logical/physical): 512B/512B Partition Table: gpt Disk Flags: Number Start End Size File system Name Flags 1 1049kB 2147GB 2147GB primary
- Running lsblk will show that vdb1 partition has been created. This partition is actually what will have the filesystem to allow us to access it.
$ lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT vda 253:0 0 40G 0 disk └─vda1 253:1 0 40G 0 part / vdb 253:16 0 2T 0 disk └─vdb1 253:17 0 2T 0 part
- Format with the ext4 filesystem using `mkfs`on /dev/vdb1 (not /dev/vdb). vdb1 is the partition that was created using parted. When formatting a device with a filesystem, you want to do it on a partition and not on the whole disk.
$ sudo mkfs -t ext4 /dev/vdb1 mke2fs 1.42.9 (28-Dec-2013) Filesystem label= OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) Stride=0 blocks, Stripe width=0 blocks 131072000 inodes, 524287488 blocks 26214374 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=2671771648 16000 block groups 32768 blocks per group, 32768 fragments per group 8192 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968, 102400000, 214990848, 512000000 Allocating group tables: done Writing inode tables: done Creating journal (32768 blocks): done Writing superblocks and filesystem accounting information: done
$ sudo parted /dev/vdb $ # vdb is the disk name for this specific case. Check by running lsblk for your disk name for the volume. (parted) print Error: /dev/vdb: unrecognised disk label Model: Virtio Block Device (virtblk) Disk /dev/vdb: 10.5TB Sector size (logical/physical): 512B/512B Partition Table: unknown (parted) mklabel gpt (parted) print Model: Virtio Block Device (virtblk) Disk /dev/vdb: 10469GB Sector size (logical/physical): 512B/512B Partition Table: gpt Disk Flags: Number Start End Size File system Name Flags (parted) mkpart primary 0GB 10469GB (parted) print Model: Virtio Block Device (virtblk) Disk /dev/vdb: 10469GB Sector size (logical/physical): 512B/512B Partition Table: gpt Disk Flags: df -h Number Start End Size File system Name Flags 1 0.00GB 10469GB 10469GB primary
Create a ext4 filesystem for the partition. ext4 is a filesystem type.
Create ext4 filesystem $ sudo mkfs -t ext4 /dev/vdb mke2fs 1.44.1 (24-Mar-2018) /dev/vdb contains a ext2 file system    last mounted on /mnt/volume1 on Thu Sep 20 22:03:23 2018 Proceed anyway? (y,N) yes Creating filesystem with 2555904000 4k blocks and 319488000 inodes Filesystem UUID: b8a711b5-1929-4f20-92df-71568a930ea7 Superblock backups stored on blocks:    32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,    4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968,    102400000, 214990848, 512000000, 550731776, 644972544, 1934917632 Allocating group tables: done                           Writing inode tables: done                           Creating journal (262144 blocks): done Writing superblocks and filesystem accounting information: done
Mount the filesystem found in vdb at a mountpoint. Check that you can actually access it by running `ls` and writing a file there.
$ sudo mkdir /mnt/volume1 $ sudo mount /dev/vdb /mnt/volume1 Test creation of large file within /mnt/volume1. Size is different than what intended because the dd process was stopped early. $ sudo dd if=/dev/zero of=large2.txt bs=1M count=50000 $ ls -lh total 32G -rw-r--r-- 1 root root 32G Sep 20 22:05 large2.txt drwx------ 2 root root 16K Sep 20 21:29 lost+found
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