During the last week I was working with my colleague Nikolay Nikolov on a VDI design solution using IBM FlashSystem storage. The old solution using SSD local disks was experiencing the login time for VDI users up to 4 mins. After case analyzing we found high number of IOPS which was leading to full queue of the RAID controller and the SSD was not able to handle during the login storm. The FlashSystem storage was ordered to replace the SSD local storage as it provides maximum IOPS up to 1,100,000 and to enable the vSphere enterprise features such as vMotion, DRS, HA.
Within the design we had to integrate the IBM FlashSystem recommendation settings for ESXi. Two important points we found and addressed in the design [Multipath settings & Sector size].
1. Multipath settings
For each storage device, the ESX/ESXi host sets the path selection policy based on the claim rules defined in the /etc/vmware/esx.conf file. By default, VMware supports the following path selection policies:
- Fixed (VMW_PSP_FIXED),
- Fixed AP (VMW_PSP_FIXED_AP),
- Most Recently Used (VMW_PSP_MRU),
- Round Robin (VMW_PSP_RR).
The default Storage Array Type (SATP) is VMW_SATP_DEFAULT_AA and default Path Selection (PSP) is Fixed (VMware) for flash volume and it has four paths:
To get better performance from the IBM FlashSystem, from the Path Selection drop-down list, select Round Robin (VMware):
Follow similar steps for all the flash volumes to update their multipath settings.
To change the default value of Path Selection (PSP) to Round Robin (VMware) and set the default value of Storage Array Type (SATP) to VMW_SATP_DEFAULT_AA, use the following commands:
- ESXi 4.1: esxcli nmp satp set -P VMW_PSP_RR -s VMW_SATP_DEFAULT_AA
- ESXi 5.X: esxcli storage nmp satp set -P VMW_PSP_RR -s VMW_SATP_DEFAULT_AA
Also, In order to achieve the best performance in VMware and FlashSystem environments, it is recommended to change the IOPS parameter of VMW_PSP from 1000 to 4. This can be done by using the esxcli commands for each volume on each host. Refer to the following example to update PSP_RR:
- ESXi 4.1: esxcli nmp roundrobin setconfig -d [device UID] -t iops -I 4
- ESX 5.X: esxcli storage nmp psp roundrobin deviceconfig set -d [device UID] -t iops -I 4
Note: This actions need to be done from VMware side
2. Sector size guidelines for VMware
With traditional spinning disk, a sector refers to a physical part of a disk. The size of the sector is defined by the disk manufacturer and most often set to 512 bytes. The 512 byte sector size is supported by most operating systems.
FlashSystem 840 does not have fixed physical sectors such as spinning disks. Data is written in the most effective way on flash. The sector size, however, is the same as the traditional spinning disk sector size to maintain compatibility. Therefore, the sector size presented to the host by the FlashSystem 840 is 512 bytes.
ESX does not support a sector size of 4 KB. All flash volumes must be configured with a 512-byte sector size for VMware.
Note: This actions need to be done from Storage side
For more information about Deploying IBM FlashSystem 840 in VMware ESXi environments check this link
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