White Papers

Performance tuning
46 Dell EMC SC Series: Red Hat Enterprise Linux Best Practices | CML1031
4.5.3 nr_requests
This value is used by the Linux kernel to define the depth of the request queue and is often used in
conjunction with changes to the HBA queue depth configuration. The default for RHEL 6 and 7 is 128 while
256 is the new default in RHEL 8. The value can be adjusted using the procedures similar to section 4.5.2.
It is recommended to lower the value for latency-sensitive applications. Consult the Red Hat Performance
Tuning Guide on Red Hat Enterprise Linux Document Portal for more information.
https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/
4.5.4 max_sectors_kb
max_sectors_kb determines the number of kilobytes that the block layer will allow and accept according to
the filesystem request. This value must remain equal to or smaller than the maximum allowable size dictated
by the hardware layer. Typically, max_sector_kb is automatically set to the page size in the SC Series
storage system which is the recommended setting. An SC Series page size can be 512k, 2M, or 4M.
Show the current max_sectors_kb value:
# multipath -ll | sed -rn 's/.*(dm-[[:digit:]]+|sd[[:alpha:]]+).*/\1/p' | xargs
-I % echo egrep -H \"*\" /sys/block/%/queue/max_sectors_kb |bash
/sys/block/dm-2/queue/max_sectors_kb:512
/sys/block/sdb/queue/max_sectors_kb:512
/sys/block/sdd/queue/max_sectors_kb:512
/sys/block/sdc/queue/max_sectors_kb:512
/sys/block/sde/queue/max_sectors_kb:512
Show the SC page size in DSM GUI:
In DSM, under the Storage tab, select Storage Types on the left pane and expand the tree. See Figure 3.
SC Series page sizes