IBM Storage Scale with IBM® FlashCore Modules (FCMs) drives

Starting from version 5.1.6, IBM Storage Scale supports compression-enabled FCM 3.0 drives (or higher).

FCM drives are capable of data compression with no performance penalty. The data compression ratio can vary depending on the generation of the FCM and the data or file types that are being written to the drive. Due to the indeterminable nature of data compression, it is possible to run out of physical space for the file system created from the FCM.

IBM Storage Scale FCMs are a family of high-performance flash drives in a standard form factor of 2.5 inches, 15 millimeters. The FCM design uses the NVMe protocol, a PCIe Gen 3 U.2 interface, and high-speed NAND memory to provide high throughput and input/output operations per second with consistent and predictable latency.

FCM drives support of IBM Storage Scale is built on IBM Storage Scale RAID technology so that users can only deploy an IBM Storage Scale file system on FCM drives by using an IBM Storage Scale System. This support introduces space monitor capability, which is meant to monitor the physical space utilization of the declustered array (DA) that is created from FCM drives.

Note: The space monitor is available and enabled for FCM drives only on an IBM Storage Scale System.

The FCM features hardware-based, real-time inline data compression and self-encryption that provides consistent compression and encryption across the full range of workloads and with no performance penalties. By using FCM, usable capacity can be significantly increased while maintaining consistent application performance. FCM can substantially reduce costs for storage acquisition, rack space, power, and cooling; FCM also contributes to extend the life of existing storage assets.

When connected, the IBM Storage Scale System recognizes the presence of FCM drives and starts space monitoring. This capability monitors the space utilization of the DA that was created from the virtual disk. When a file system is created out of those virtual disks, IBM Storage Scale treats the FCM drives the same way as it treats the NSDs with thin-provisioning enabled, and the emergency space gets reserved for the file system.

Note: For the space monitor capability, refer to IBM Storage Scale System 3500 and IBM Storage Scale System 6000 documentation.

The following example shows how to specify a stanza for the NSD-based of an FCM drive:

%nsd:                                                           
nsd=gpfs1nsd                                                    
usage-metadataOnly                                              
pool=system                                                     
thinDiskType={nvme|auto}

For an IBM Storage Scale System with FCM drives, a stanza file can be used. However, creating a file system with the stanza file is not a typical practice; instead, the deployment is done through automated scripts and the file system is created then. The script has thinDiskType automatically configured so that the administrator does not need to manually set up thinDiskType. For more information, see IBM Storage Scale System Deployment Guide (and instructions for the new deployment of an Elastic Storage Server).

Configuration

For a file system that consists of FCM drives, a new set of control variables are introduced to control the behavior of the file system with FCM drives in the context of space monitoring and space reclaim.

For the DA, physical space states are defined for the space monitor. These states are incremental and defined as: Good (first physical space state), Info, Warning, Critical, and OOS (out-of-space). As the space of each DA is filled with data, a state progresses higher up until it reaches the next state.

2024-05-10_15:36:36.830-0400: [I] Command: successful mount essfs1    
2024-05-10_15:36:39.338-0400: [I] DiskSpaceState transitioned from Invalid to Good for essfs1 pool 0, bg reclaim config (mode/threshold/interval/rate) changed to: 1/10/60/1

Note: For more details about the physical space states, see IBM Storage Scale System 3500 and IBM Storage Scale System 6000 documentation.

As the compression ratio can vary depending on the file types that are being written to the FCM drives, it is important to manage and monitor the physical space utilization and the state.

The space monitor, when IBM Storage Scale is initializing, gets automatically enabled and started if the presence of FCM drives is detected on an IBM Storage Scale System.

Deployment recommendation

Data reduction storage types like FCM and thin-provisioned storage systems share the concern about the possibility that the device might run out of physical space on a drive (or a LUN or a volume that is created from the drive).

In addition to existing features that mitigate the out-of-space handling or recovery, IBM Storage Scale provides a feature called graceful emergency recovery for FCM.

For more information, see Graceful emergency recovery.