Rethinking Cloud Storage?
The purpose of this article is present Software Defined Storage (SDS) technology called vSAN, which is an excellent alternative to the Dedicated Servers used for storage and hardware-defined SAN appliances. It is used by some VMware-based providers of Cloud Servers to design high performance and reliable storage solutions.
The Virtualization and Cloud computing solution producer VMware announced a software defined storage solution called vSAN. It went on general availability in March, 2017. Lets take a look at the this software defined storage solution and see how it works and how it changes the Cloud Storage.
What is vSAN?
vSAN is an alternative to vendor lock-in Software Area Networks (despite being itself a vendor lock-in software) as it is implemented at the kernel level. It is built for enterprise use and its purpose is to take local storage located in individual servers and turn it into shared storage area network that can be used by Hight Availability, vMotion and other services of VMware.
vSAN is implemented at the cluster level and can be enabled in two simple steps. The administrators can define storage policies that guarantee virtually 100% availability of the Cloud services. vSAN is scalable and allow system administrators to add additional 42 storage drives within an ESXi host and scale it out by simply adding another 32 storage nodes into the cluster.
vSAN’s Requirements
vSAN requires 3–32 storage nodes per vSphere cluster; Hight Availability must be enabled for the cluster; 1 SSD and 1–7 spinning HDDs, that create a disk group; 1 GbE minimum, with 10 GbE recommended; vSphere and vCenter; VSAN license key. The license is required as vSAN is a proprietary commercial SDS soltuon.
The SSD storage is used for caching only in the vSAN. The best practice says that 10% of the storage space in each disk group must be SSD to ensure there is enough space for caching. Each host can have 0 to 5 disk groups. Any host with zero disk groups can run Cloud Servers like other hosts, but storage requests will go to the other vSAN nodes.
The vSAN has been tested with 2 million IOPS in a single cluster, and the results shown that only a 10% hit to CPU performance. Any VMware ESXi based Cloud Servers usually run around 50% CPU utilization. An extra 10% hit would not affect their performance. Each vSAN storage cluster supports up to 4400 terabytes of storage. This space is given directly to vSAN to use.
How Does vSAN work?
It maximizes available storage space. It is implemented at the VMkernel level to maximize performance. This requires SSD drives for caching to maximize disk performance. It also requires low latency interconnect, for example a 10 GbE internal network. To maximize space, all Virtual Machine Disk (VMDK) files are thin provisioned and no parity or mirroring RAID is employed on the hosts. Capacity can be increased by adding SSDs or HDDs to a host and giving vSAN access to the new ones.
If the High Availability function is active, the systerm administrators need to temporarily disable to configure the vSAN. vSAN get the disks it needs to work either automatically or manually? Automated option means that vSAN will automatically use all the SSD or HDDs, not used elsewhere in the system and will create disk groups automatically. It is also possible to manually configure the storage disk groups in order to have more control over them.
Storage Policies
vSAN turns any local storage into shared network storage. It allows the adminitrators to setup and apply different policies to the Cloud Servers and storage system automatically enforces them.
A single policy is created and used by everything that uses vSAN. It is configured to tolerate the loss of a host, storage drive, or disk group by setting Failures to Tolerate to one.
vSAN looks at the storage policy assigned to each Cloud Server and automatically applies it, placing each .vmdk file on disks it chooses. If the system is set to tolerate one failure, vSAN would create 2 copies of the disk, each on a separate host.
How Does vSAN Handle Failures?
vSAN is a fault-tolerant and keeps operating in the event of a single srotage disk, network, or server failure. Its failover functionality depends on the storage policies. There would be no data loss in any case as writes are not acknowledged to the Cloud Servers until all copies on all underlying data hosts have completed the writing process.
