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With this USB stick as my witness: Microsoft's Storage Spaces cluster pool now Olympic-sized

Virty disk software quadruples max raw capacity per server

Microsoft has quadrupled Storage Spaces capacity and made other improvements for IoT edge use.

Storage Spaces is a way of virtualising disk capacity by aggregating drives in a pool from which virtual disks can be provisioned. These virtual disks can have RAID-like protection such as two and three-way mirrors, parity, which is like RAID-5 protection, and mirror-accelerated parity (volumes are part-mirror and part-parity). Storage Spaces work at PC, server and cluster level.

It is like VMware's vSAN when clustered servers are involved and provides file access behind a Windows File Server.

The Storage Spaces Direct updates are detailed here and include:

  • A leap to 4PB pooling for a Storage Spaces Direct Cluster in Windows Server 2019 (WS 2019) from the 1PB limit in Windows Server 2016
  • Support for 64 volumes in WS 2019, up from 32 in WS 2016
  • Support for 64TB volumes, up from 32TB
  • Maximum raw capacity per server goes up from 100TB to 400TB
  • Support for two-node clusters with USB thumb drive as the witness in split-brain situations

When there is a communications breakdown with a two-node cluster, both nodes try to own the workload and end up writing to the same disk, which can corrupt data. So a third entity is needed to force one of the nodes to cede control to the other. This entity, called a witness by Microsoft, could be either a File Share Witness or an Azure Blob in WS 2016.

The low-cost USB thumb drive witness support in WS 2019 is said to be good for IoT edge deployments because they don't necessarily have access to the Azure cloud or other Windows infrastructure for a file share. The thumb drive is inserted into a socket on a router, which has SMB 3.0 support, connecting the two drives.

Storage Spaces Direct WS 2019 has also been given the ability to detect drives with extra long latency. All IOs are monitored and those that exceed the average latency for the drive, against similar drives, or have an excessive score in the 99th percentile, are logged and admin staff are alerted via Power Shell and Windows Admin Center.

Another change is that mirror-accelerated parity volume performance in WS 2019 is more than twice that of WS 2016.

There is a Storage Spaces Direct reference architecture for WS 2019 with server kit available from DataON, Dell EMC, Fujitsu, HPE, Inspur, Lenovo, NEC, QCT and Supermicro. There is a Windows Server Software-defined (WSSD) web page about this.

These changes will be welcomed by WS 2019 users and provide a reason to upgrade for WS 2016 users. ®

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