I recently had someone puzzled by the fact that although he has two interconnected disk-hate SSD of 512GB, it sees only one disk for storage space. Maybe he doesn't know what 2x 512GB means NVMe SSD with RAID 1 on the web server and what this storage architecture entails.
If you are a novice in managing storage spaces on a server or a simple computer, in this tutorial you will learn about NVMe and what RAID entails. Let's take it one at a time and see why in two disk-s interconnected you only see the storage space from only one.
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What does it mean NVMe (Non-Volatile Memory Express)?
NVMe comes from (Non-Volatile Memory Express) and is a protocol for interconnecting storage devices, such as SSDSites (Solid State Drives) or Flash storage modules (USB Stick, memory stick). This protocol is specially designed to exploit the high performance of flash memory based storage devices and is mainly used for high performance storage devices. They are most often used in the architecture of web servers or database storage systems. Where high write/read speed is required.
Unlike traditional storage interfaces such as SATA, NVMe uses a connection PCI Express (PCIe) to allow faster data transfers between the computing system and the storage devices. NVMe also uses an architecture of the "queueing” which allows several read and write operations to be processed simultaneously, which leads to an increased performance and efficiency of the storage system.
What does it mean 2x 512GB NVMe SSD cu RAID 1?
Here is the so-called problem where you only see one storage space. Although with a simple calculation made by a novice, two disk-s of 512GB, would mean a total of 1TB free space for storage.
In the case of web servers, the security of stored data is very important. That is why they are used disk-hate SSD interconnected NVMe with software RAID 1. If a motherboard, memory or even CPU can be replaced without data loss, if a disk breaks down, the effects can be catastrophic.
What does RAID 1 mean?
RAID (Redundant Array of Independent Disks) is a data storage software / technology that combines several diskphysical features to achieve better performance and safety. It is a kind of binder of physical storage units that are interconnected in a system.
Several types of RAID are available, which adapt to the requirements of each configuration. In the case of web servers, the best and most cost-effective choice is RAID 1.
What does 2x NVMe SSD with RAID 1 mean?
RAID 1 is the "mirror of data" on a disk. Mirroring. The data is duplicated on two identical disks, which ensures redundancy and if one of the disks fails, the data is still available on the other disk. Thus, the data is protected in case of damage. Reading performance is improved, but writing performance is slightly affected.
For web servers, data protection and reading speed are the top features of a disk. Therefore, 2x NVMe SSD with RAID 1 is a good choice for web servers, where read speed is more important than write speed. Yes, it can be a disadvantage when the cache system is chosen diskthe but REDIS, memcached and others, use RAM cache. (Another discussion).
If you want, RAID 1 helps to create a kind of disk backup. This does not mean that if you accidentally deleted data from disk, with RAID 1 you will be able to recover them from the other disk. It is only about if one of the disk-s breaks down.
In conclusion, it is normal for the disks in a RAID set to be seen by the operating system as a single disk. In the case of one RAID 1, the data is replicated on both disks in the set, so the available space will only be equal to the space of a single disk, but the data will be redundant and secured in case one of the disks has a failure.
Custom made: "df -h” executed in a server with Linux, it will only display the currently mounted / partitioned and used storage space on each file system. If the partitions on the second disk are not mounted in the file system, then they will not be displayed in the command result. To check available disks and existing partitions, you can use the command: fdisk -l or lsblk.
In conclusion, if you have two on a server or a computer disk-hate NVMe SSD with RAID 1, you will only have available for storage a volume equal to that of a single one disk.
