PowerScale: Using 'dd' on the node CLI to troubleshoot the source of latency.

Summary: You can use the 'dd' command on a PowerScale node CLI to help determine the source of the bottleneck for a particular performance issue. For example, if you can replicate the latency directly on a node command line using 'dd' then this indicates an issue at the file system layer vs. the protocol (NFS or SMB) or networking layer. ...

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Instructions

Here are tips on using the 'dd' command on a PowerScale node:

Being that our on-disk block size is 128k in OneFS, Dell Support recommends using the 'bs=128k' option (bs = block size) when using the 'dd' utility. This should be sending data to disk when 'dd' has enough to fill a full block.

Write speed test: 1GB file
 

# dd if=/dev/zero of=/ifs/data/Isilon_Support/1GB.out bs=128k count=7812


Write speed test: 10GB file
 

dd if=/dev/zero of=/ifs/data/Isilon_Support/10GB.out bs=128k count=78120


Read Speed Test:

For a read speed test, the 'cp' (copy) command is sufficient for testing:
 

# time cp /ifs/data/Isilon_Support/kevin1GB.file  /ifs/data/Isilon_Support/cptestfile


Optionally, you can use the 'dd' utility as follows:
 

# dd if=/1GB.file of=/1GBoutput.file bs=128k
# dd if=<actual filename you are reading>  of=/ifs/data/Isilon_Support/file.out  bs=128k


Here are some typical baselines, as tested in our lab:

Hardware: F800-4U-Single-256GB-1x1GE-2x40GE SFP+-24TB SSD

WRITE
 

1G
Isilon-5# dd if=/dev/zero of=/ifs/data/Isilon_Support/1GB.out bs=128k count=7812
7812+0 records in
7812+0 records out
1023934464 bytes transferred in 1.037575 secs (986853056 bytes/sec)  ---> 1GB/sec

10G
Isilon-5# dd if=/dev/zero of=/ifs/data/Isilon_Support/10GB.out bs=128k count=78120
78120+0 records in
78120+0 records out
10239344640 bytes transferred in 9.491726 secs (1078765328 bytes/sec) ----> 1GB/sec

 

READ
 

1G
Isilon-5# time cp /ifs/1GB.out /ifs/data/Isilon_Support/kevintest22
cp -i /ifs/1GB.out /ifs/data/Isilon_Support/kevintest22  0.01s user 1.57s system 84% cpu 1.859 total

10G
Isilon-5# time cp /ifs/10GB.out /ifs/data/Isilon_Support/kevintest24
cp -i /ifs/10GB.out /ifs/data/Isilon_Support/kevintest24  0.02s user 15.92s system 85% cpu 18.604 total



Parameter Definitions:

of = name of output file. Confirmed has *nothing* to do with size.
bs = block size    1024 = 1Gb   10024 = 10Gb
Count = copies only this number of blocks. (default is for dd to keep going forever)
if = read from FILE instead of stdin

To summarize, you end up with a file of size = 'bs x count'.

Affected Products

Isilon, Isilon A2000
Article Properties
Article Number: 000206300
Article Type: How To
Last Modified: 02 مارس 2026
Version:  3
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