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b4ndit
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Dedup and Compress for all flash - disk design consideration

Hi all,

I want to ask about design consideration for dedup and compression features enabled for vsan all flash.

This consideration start from cormac article..

http://cormachogan.com/2016/02/12/vsan-6-2-part-1-deduplication-and-compression/

Other considerations
The first thing to note is that deduplication and compression is only available on all-flash VSAN configurations. The second this to note is that this feature will make you reconsider the way you scale up your disk groups. In the past, administrators could add and remove disks to disk groups as the need arose. While you can still add individual disks to a disk group as you scale up, the advice is, if you plan to use deduplication and compression, build fully populated disk groups in advance. Then enable the space efficiency techniques on the cluster. Because the hash tables are spread out across all the capacity disks in a disk group when deduplication and compression are enabled, it is not possible to remove disks from a disk group after the space savings features are enabled. It should also be taken into consideration that a failure of any of the disks in the disk group will impact the whole of the disk group. You will have to wait for the data in the disk group to be rebuilt elsewhere in the cluster, address the failing component and recreate the disk group, followed by a re-balance of the cluster. These are some of the considerations you will need to take into account from an administrators perspective when leveraging the saving capacities of deduplication and compression on VSAN.

So,

1. What is the effect of adding another data disk in a disk group with dedup and compression enabled accross the cluster ?

2. Hash table will spead accoss the data disk. What if we start with 1 disk group and then add another disk group in similar configuration. What the effect that would happen ?

3. How can we monitor the data in the disk group rebuilt else where in the cluster has been completed ?

Thanks

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