PowerScale: OneFS: Unexpectedly low write throughput when using continuous availability

Summary: Unexpectedly low write throughput when using continuous availability with SMB protocol.

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Symptoms



Write throughput may be unexpectedly low when using continuous availability (CA) over SMB. CA, by default, uses synchronous writes:

  
# isi smb shares view CA | grep "Ca Write"
                Ca Write Integrity: write-read-coherent

write-read-coherent
Writes to the share are moved to persistent storage before a success message is returned to the SMB client that sent the data. This is the default setting.

Cause

If a user uses SMB CA and has write I/O that is mostly sequential in nature, the Endurant Cache (EC) should be disabled. This should be done on the SMB CA share to ensure performance. Once the EC is turned on, SMB CA on Isilon will store stable writes on EC across the Isilon nodes first which could cause EC to be a potential bottleneck. EC can lower the average latency for small and random stable writes workloads. However, EC can become a bottleneck when writes are stable and sequential. If the users write I/O is mostly small and random, the EC should remain on. If there is a combination of sequential and random write I/O, additional tests are important to determine the correct setting for EC on that SMB CA share.

Reference: See bottom of page 34 in section 2.1.3: https://www.delltechnologies.com/asset/en-us/products/storage/industry-market/h17463-powerscale-design-and-considerations-for-smb.pdf

Resolution

If CA is not needed, the share would need to be re-created without it or test performance in a test share without CA. If there is no performance difference, then there could be many reasons for slow performance which would need to be investigated separately.

The following commands may be used to test disabling EC:
  • Disable EC on cluster globally (enabled by default):
isi_sysctl_cluster efs.bam.ec.mode=0
  • Disable EC on a specific directory (enabled by default):
isi set -c off  <path to directory>

The above command also disables coalescer. For test purpose only, if you want to disable EC on a path and keep the coalescer on, using command:

isi set -c coal_only  <path to directory>
			
			
Reference:
https://www.delltechnologies.com/asset/en-us/products/storage/industry-market/h17463-powerscale-design-and-considerations-for-smb.pdf

Affected Products

PowerScale OneFS

Products

Isilon, PowerScale OneFS
Article Properties
Article Number: 000067443
Article Type: Solution
Last Modified: 15 Dec 2025
Version:  4
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