ESS Limits and RAM Usage:

Limits

ESS supports disks and arrays up to 16 PB. The size and granularity of the block mapping table varies depends on the effecive size of the backing array. The map balances memory usage and compression rounding. Blocks are compressed and then rounded up to fixed boundaries. This rounding reduces the compression effectiveness in exchange for lowering memory usage.

Array Mapping Granularity

Array Size	5 Byte MAP	Max LBA Size	6 Byte MAP	Max LBA Size
1 TB	99.2%	16 TB	99.9%	256 TB
4 TB	98.4%	32 TB	99.9%	512 TB
16 TB	96.8%	64 TB	99.8%	1 PB
64 TB			99.6%	2 PB
256 TB			99.2%	4 PB
1 PB			98.4%	8 PB
16 PB			96.9%	16 PB

Memory Usage

Buffer Memory

You can tune the buffer usage based on your performance needs. This can vary from 2GB to 8GB of buffer RAM.

MAP Memory Usage

The map requires one entry for every 4K logical block. This is based on the logical size of the array. This defaults to 95% of the physical size, but you can over-provision the array if your data is compressible.

MAP Size	MAP Ram Usage
5	1.25 GB/TB
6	1.50 GB/TB