43 | Dell EMC VxRail Appliance Operations Guide
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VxRail deduplication and compression
VxRail All-Flash configurations offer advanced data services including deduplication and
compression.
For many environments, data deduplication and compression can significantly increase usable
storage capacity. When configured on VxRail, vSAN deduplication and compression occurs
inline when data is de-staged from the cache tier to the capacity tier. Data is first de-duplicated
by removing redundant copies of blocks that contain the exact same data and then compressed
before writing the data to disk. While all VMs are unique, they often share some amount of
common data. Rather than saving multiple copies of the same data, identical blocks are saved
once, and references to the unique blocks are tracked using metadata maintained in the
capacity tier.
The figure below shows how data is deduplication inline before it written to the capacity drives
on VxRail.
Figure 19. Inline data deduplication
The de-duplication algorithm is applied at the disk-group level and results in a single copy of
each unique 4K block per disk group. While duplicated data blocks may exist across multiple
disk groups, limiting the de-duplication domain to a disk group does not require a global lookup
table. This minimizes network overhead and CPU utilization, making VxRail deduplication very
efficient.
LZ4 compression is applied after the blocks are deduplicated and before being written to SSD. If
the compression results in a block size of 2KB or less, the compressed version of the block is
persistently saved on SSD. Otherwise, the full 4KB block is written to SSD.
Summary of Contents for VxRail Appliance
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