vSAN has introduced a concept of vSAN Disk Group.
A disk group is nothing but a logical container of storage where multiple disks (SSD or HDDs) are present. Each host participating in a vSAN Cluster has local disks configured in a disk groups. vSAN uses these disk groups to form a single datastore.
In each of these disk group, SSD primarily serves as a read cache, write buffer. While HDD's are used for persistent storage. Depending on the types of disks you select you can configure vSAN in two different ways, a hybrid configuration and an all-flash configuration. The hybrid configuration uses server-based flash devices to provide a cache layer for optimal performance while using magnetic disks to provide capacity and persistent data storage. Whereas All-flash configuration uses flash disks for both the caching layer and capacity layer.
A few things to understand about disk groups:
Each host that contributes storage in a vSAN cluster will contain at least 1 disk group.
Disk groups contain at most 1 cache device and between 1 to 7 capacity devices.
A vSAN host can have maximum of 5 disk groups, each containing up to 7 capacity devices, resulting in a maximum of 35 capacity devices for each host.
Whether hybrid or all-flash configuration, you must have one cache device and it must be a flash device.
In a hybrid configuration, the cache device is utilized by vSAN as both a read cache (70%) and a write buffer (30%).
In an all-flash configuration, 100% of the cache device is dedicated as a write buffer.
If a Cache tier disk is failed then the whole disk group is considered as failed.
If any capacity disk failed then the vSAN will wait for 60 minutes to come back for that disk. If it doesn't comes back then vSAN will try to recreate the missing components and rebalance the cluster.
To create a Disk Group on a Host -
1. Navigate to the vSAN cluster.
2. Click the Configure tab.
3. Under vSAN, click Disk Management.
4. Select the host and click Create disk group.
5. Select the flash device to be used for cache.
6. Select the type of capacity disks to use, depending on the type of disk group you want to create (HDD for hybrid or Flash for all-flash).
7. Select the devices you want to use for capacity.
8. Click Create or OK to confirm your selections.
That's it for now.
I hope you will find this post informative.
Thank you for reading!
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