Open-ESS - Integrated All-Flash SAN/NAS

Open-ESS integrates the ESS block-level linearization stack into an easy to install SAN/NAS appliance software package. Based on the widely used Open-E DSSv7 SAN/NAS package.  Open-ESS brings best-of class Flash performance to low cost SAN/NAS deployments.

CPUs:  Nearly any server-class CPU will work with Open-ESS.  CPUs that don't support ECC memory are not recommended.  Otherwise, it is an exersize in performance and cost.

The E3-1200 series is an excellent entry level CPU.  Important limits are the number of PCI-e channels and limited amount of RAM.  In general, these CPUs only have enough PCI-e channels to support 8-12 SSDs and a single high-speed network interface.  In terms of RAM, the older versions of these CPU had a limit of 32GB.  Newer version have increased this limit to 64GB.

The E5-1600 series is the current main-stream single socket Intel Xeon CPU.  It is an excellent choice for Open-ESS and can support 24+ SSDs and 3+ high-speed networking adapters.  RAM support above 256GB lets you bulid very large arrays.

The E5-2600 series is the dual-socket version of the E5-1600 series.  Dual socket servers work well with Open-ESS, but the dual socket nature is often overkill for Open-ESS applications.  While the dual socket servers have more slots and more memory capacity, the complexity of a dual socket system tends to make them equal in perforamnce to single socket servers.

You can usually use E5-2600 CPUs in single socket motherboards.  You can also usually populate a dual socket motherboard with only a single CPU.  Just be aware of what is supported and what functionality is lost of a motherboard with a CPU missing.

RAID Levels:  ESS arrays can be configured for RAID-5 or RAID-6.  Other RAID levels offer inferior performance and/or wear compared to RAID-5 or RAID-6.  RAID-0 is not supported as we believe that at least a single drive failure must be tolerated.  RAID-1 and RAID-10 are not supported as RAID-5 and RAID-6 are actually faster, produce less Flash wear, and yield more usable space.

The recommended RAID level is for RAID-5 for 8 SSDs and lower, and RAID-6 for 16 SSDs and higher.  This is only a recommendation and you can choose your own configuration.

Compression:  ESS support block-level compression.  In most cases, best performance and drive life is experienced with compression enabled.  Some specific workloads, like media production with very large uncompressible files may perform better with compression disabled.

Hot Spares:  You can configure the ESS array with from 0 to 2 "hot spare" SSDs.  A hot-spare will automatically replace a failed drive without interversion.  The default is for 0 hot spares.

Usable Disk Space:  ESS arrays have a 10% "overprovisioning" value.  With Open-ESS, this value is not changable.

Calculating usable disk space is:

( number_of_drives - number_of_parity_drives - number_of_hot_spares ) * drive_size * 0.9

So an 8-drive RAID-5 array with 1TB drives will yield:

( 8 - 1 - 0 ) * 1TB * 0.9 = 6.3 TB

RAM:  ESS requires RAM to manage block-level mapping of the array.  This RAM is over and above the RAM requirements for DSSv7.  The RAM allocation in Open-ESS is very conservative, trying to insure that if your system boots, it will operate with zero possibilitiy of an "out of memory" situation.  As such, you should use the following calculation for RAM required for DSSv7 + ESS.

DSSv7 - 8GB minimum
ESS - 5 GB + 1.5 GB per TB of usable Flash space

So the above array example requires:

8GB for DSSv7
5GB base for ESS
6.3 * 1.5 = 9.45 GB for ESS mapping tables
19.3 GB total

Depending on your system configuration, this will likely require you to populate your system with 24GB or 32GB of RAM.

HBAs:  Open-ESS works with disk "Host Bus Adapters".  "Hardware RAID Cards" are not supported in RAID mode.  Some hardware RAID cards can be re-flashed as HBAs or can be programmed to present drives as single drives to the host.

Depending on the configuration, you can usually plase as many as 12 SSDs on a single HBA that is plugged into an 8-lane PCI-e slot and achieve full performance.

SSDs:  Open-ESS works with most SAS and SATA SSDs at full performance.  Some SSDs that features internal compression or de-duplication can experience a performance fall-off and are not recommended.  SSDs that have "write burst" technology are also not recommended.  You are looking for stable, low cost, SSDs that can be written to linearly at high bandwidth over time.  Random writes are not important.

Some SSDs in use are:

Samsing 830 Pro
Samsung 850 EVO
Samsung 850 Pro
Samsung SM863
Samsung PM863
Crucial BX-100
Crucial MX-300
Micron M5100DC


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