Can EVS be mounted to a physical server? How many data disks can be mounted?
Users can mount EVS disks to some elastic bare metal specifications, that is, 9 EVS disks (1 system disk + 8 data disks).
Users cannot mount EVS disks to a standard bare metal.
What are the limitations when I mount disks to a physical server?
l The disk to mount is in the same availability zone as the physical server.
l The status of the physical server is Running or Shutdown.
l If it is a non-shared disk, the EVS to mount is Available.
l For shared disks, the EVS disk to mount is in the Using or Available state.
l You cannot mount an EVS to some physical server specifications or images because they are not equipped with smart NICs or for some other reasons.
How do I determine whether I can mount EVS disks to a physical server specification?
You cannot mount an EVS disk to some server specifications because they are not equipped with smart NICs or for some other reasons. After selecting a specification, a message is displayed on the page, based on which you can determine whether you can mount an EVS to the specification.
How to change the disk identifier in the fstab file to UUID?
Background
After mounting a disk on a Linux-based physical server, change the disk identifier in the fstab file to UUID. Otherwise, the physical server fails to enter the operating system or services become unavailable after the physical server shuts down and restarts or restarts because the mount point is out of order.
Note:
UUID: Universally Unique Identifier, a 128-bit identifier used in computer systems to identify the amount of information.
Operation Steps
This topic uses the CentOS 7 operating system as an example to describe how to change the disk identifier in the fstab file to UUID.
1. Log in to the physical server as a root user
2. Run the blkid command to list the types of all mounted file systems in the current system and the UUID of the corresponding device.
$ blkid/dev/sda2: UUID="4eb40294-4c6f-4384-bbb6-b8795bbb1130" TYPE="xfs"/dev/sda1: UUID="2de37c6b-2648-43b4-a4f5-40162154e135" TYPE="swap"
3. Run the lsblk command to view the information of the disk device and locate the device name and UUID.
$ lsblkNAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTsda 8:0 0 50G 0 disk├─sda1 8:1 0 1G 0 part [SWAP]└─sda2 8:2 0 49G 0 part /
4. Run the vi /etc/fstab command to open the /etc/fstab file and press i to enter the editing mode. Change the disk identifier in /etc/fstab to UUID, and replace the device name with the corresponding UUID.
UUID=4eb40294-4c6f-4384-bbb6-b8795bbb1130 / xfs defaults 0 0UUID=2de37c6b-2648-43b4-a4f5-40162154e135 swap swap defaults 0 0
5. After the modification is complete, press Esc and type :wq to save and exit the file.
Is the name of the EVS device the same as that of the block device in the operating system?
Local System Disk Scenario
In the local system disk scenario, the EVS device name displayed on the physical server details page may be inconsistent with the device name in the operating system. This is because the operating system assigns a device name at startup based on hardware configuration and loading sequence.
We recommend that you perform operations independent of the device name in the local system disk scenario. On the contrary, you can operate an EVS using its unique identifier, such as a UUID or WWN. This prevents the impact on services caused by the change to the device name.
Cloud System Disk Scenario
In the cloud system disk scenario, the EVS device name displayed on the physical server details page may be different from the device name in the operating system. In this case, we also recommend that you operate with the unique identifier of the EVS, rather than relying on the device name.
A unique identifier enables you to more reliably identify and operate the EVS, without being affected by the change to the device name.
1.1.2. Why does the size of the EVS remain unchanged when queried in the operating system of the physical server after capacity expansion?
After the capacity of an EVS is expanded on a physical server, the operating system of the physical server may not automatically detect the change to the EVS size. This is because the operating system scans the hardware at startup and reads information about the device, including the size of the device. If the size of the EVS changes after the operating system starts, the operating system may not automatically update the size information of the device.
To solve this problem, you can manually scan the block device within the operating system of the physical server. The steps may vary depending on the operating system and hardware. The following is an example of the command to scan the sdh disk in the Red Hat system:
echo 1 > /sys/block/sdh/device/rescan
Note:
The "sdh" in the command is a sample device name. You must replace it with an actual device name.
After this command is executed, the operating system will rescan the sdh disk and update the size information of the device. Later, you can check whether the actual size of the EVS has been updated with the appropriate command or tool.
How to select a storage type?
When configuring a disk type on the Create Physical Server page, you can select a different EVS to assign a physical server based on your business needs.
Why is the capacity displayed in the physical server operating system smaller than the nominal capacity declared on the official website?
When you view the disk capacity in the operating system, the disk capacity may be smaller than the nominal capacity declared on the storage service website. The differences may be caused by the following factors:
l Difference between decimal and binary: Hardware vendors usually use decimal to calculate the capacity, while an operating system uses binary to calculate the capacity. This results in a difference between the nominal capacity and the capacity shown in the operating system.
l File system formatting: When formatting a hard disk, the file system uses some space to store metadata and file system structure. This overhead reduces the free space.
l Disk partition: The operating system plans the hard disk into multiple partitions, including boot partition, system backup and restore partition. These partitions take up some disk space.
l RAID: If RAID technology is used, such as RAID 1 (disk mirroring), the capacity of one disk is used to store redundant data to provide data redundancy and fault tolerance.
The above factors may cause the actual available capacity to be smaller than the declared nominal capacity, but these are normal and conform to the working principles of the hardware and operating system.
Commonly Used Command Lookup on Linux Operating System
lsblk
The lsblk command lists information about all available block devices and also shows dependencies between them, but does not list information about RAM disks. Block devices include hard disks, flash memory, CD-ROM, and so on.
The lsblk command lists all block devices in a tree by default. Open the terminal and enter the following command:
lsblkNAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTsdb 101:0 0 60G 0 disk ├─sdb1 101:1 0 14G 0 part [SWAP]└─sdb2 101:2 0 46G 0 part /sdc 102:1 0 20G 0 disk
The seven column names are as follows:
l NAME: Name of the block device.
l MAJ:MIN: Indicates the numbering of major and minor devices.
l RM: Indicates whether the device is removable. "0" indicates no and "1" indicates yes.
l SIZE: Indicates the capacity size of the device.
l RO: Indicates whether the device is read-only. "0" indicates no and "1" indicates yes.
l TYPE: Indicates whether the type of the block device (disk or a partition on the disk).
l MOUNTPOINT: Indicates the mount point to which the device is mounted.