I initially held off reviewing E8 Storage as we had a podcast scheduled with CEO Zivan Ori, which went live last Friday.  Rather than make assumptions about the technology, I wanted to ensure I was giving some credit to the architecture.  I’m glad I did wait because there were one or two fundamentals I hadn’t fully understood.

E8 Architecture

First, I should point out that E8 Storage is a dis-aggregated design, with centralised physical storage and functionality devolved to client servers.  The E8 platform uses two core technologies – NVMe flash drives and RDMA.  NVMe provides access to high-IOPS flash storage, with lots of parallelism.  Compared to SAS/SATA, NVMe has many more queues (64K) and greater queue depth (64K).  This allows NVMe to handle more I/O requests in parallel – perfect for a dis-aggregated architecture.

RDMA provides the other piece of the puzzle.  Client servers can access metadata on management controllers that map out the usage of NVMe drives.  This is achieved at high speed/low latency using RoCE (RDMA over Converged Ethernet).

Contrasting Legacy Architectures

How does this contrast to traditional legacy architectures?  With dual-controller architectures, all data has to pass through one or more controllers.  The bottleneck is the ability to manage the I/O throughput when serving many clients (host servers).  The result is the inability to fully utilise NVMe performance.  These issues weren’t as obvious with SAS/SATA flash and hard drives.

E8 writes to NVMe drives directly, bypassing the need to write through a shared controller.  This results in extremely low latency and high throughput.  The disadvantage for this kind of architecture is the shared controller architecture also provided shared metadata and consistency on metadata changes.  E8 achieves this by allowing client devices to talk to the metadata servers directly over RDMA.

The Architect’s View

You can listen to the podcast here, which has plenty of good additional background.  Don’t forget also to tune in to Storage Field Day 14 (details here) and get the full detail on E8.

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Written by Chris Evans