Low Disk Performance with high IO stalls system
This document (7023297) is provided subject to the disclaimer at the end of this document.
SUSE Linux Enterprise Server 11
This could be an indication that there is
set on the Filesystem even so the underlying Device does not have a write cache.
To alleviate this issue it is recommended to mount the relevant filesystems with
as mount option.
Extreme care should be taken to ensure that the device connected to this Filesystem really has a volatile cache or not.
If it does then setting
can result in data loss. Please never set nobarrier on a Filesystem on a device with cache enabled!
To identify whether the device has a cache or not, one can check
and check for "cache" like
dmesg | grep cache
and the result might look like
[ 3.685928] sd 0:2:0:0: [sda] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
[ 5.140281] sd 1:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
as can be seen the device identified as
reports the Write cache as disabled, so a Filesystem associated with this device can use
the opposite in this example is the device identified as
this device reports the Write cache enabled, so no Filesystem associated with this device should
have the barriers removed to prevent data loss.
This can also be checked in the running system with the tool
On the same system as in the example above the output of sdparm reads
belphegore:~ # sdparm --get=WCE=1 /dev/sda
/dev/sda: DELL PERC H730 Mini 4.27
which means Write Cache disabled for sda, nobarrier possible
belphegore:~ # sdparm --get=WCE=1 /dev/sdb
/dev/sdb: IFT DS 1000 Series 555Q
which means Write Cache enabled for sdb, barrier necessary
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- Document ID:7023297
- Creation Date: 23-Aug-2018
- Modified Date:03-Mar-2020
- SUSE Linux Enterprise Server
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