Administrator Guide

Solution Architecture
13 Dell EMC Ready Solution for HPC PixStor Storage | Document ID
Figure 3 SAS & High-speed cable diagram
Storage configuration on ME4 arrays.
The DellEMC Ready Solution for HPC PixStor Storage has two variants, the standard configuration and
the one that includes the High Demand Meta Data module. On the standard configuration the same pair of
R740 servers use their ME4084 arrays to store DATA on NLS SAS3 HDDs and Metadata on SAS3 SSDs. On
Figure 4 we can see this ME4084 configuration showing how are the drives assigned to the different LUNs.
Notice that each ME4084 has eight linear RAID6 (8 data disks + 2 parity disks) Virtual Disks used for DATA
only where HDDs are selected alternating even numbered disk slots for one LUN, and odd numbered disk
slots for the next LUN, and that pattern repeats until all 80 NLS disks are used. The last four disk slots have
SAS3 SSDs, which are configured as two linear RAID 1 pairs, and only hold Meta Data. Linear RAIDs were
chosen over virtual RAIDs to provide the maximum possible performance for each virtual disk. Similarly, RAID
6 was chosen over ADAPT, in spite of the advantage the later has when rebuilding after failures.
When the Storage Module has a single ME4084, then GPFS is instructed to replicate the first RAID 1 on the
second RAID 1 as part of a failure group. However, when the Storage module has 2 or 4 ME4084s, those
arrays are divided in pairs and GPFS is instructed to replicate each RAID 1 on one array on the other array,
using different failure groups. Therefore, each RAID 1 always have a replica managed by a GPFS’s failure
group.
All the virtual disks have associated volumes that span their whole size, and are mapped to all ports, so that
they are all accessible to any HBA port from the two R740s connected to them. Also, each R740 has one
HBA port connected to each ME4084 controller from their storage arrays. Such that even if one server is