I found this same thing in my EVE-NG XRv9K nodes... here's what seems to fix it.
if you are seeing the following message...
Nov 4 17:37:03.500 UTC: mediasvr[2775]: %MEDIASVR-MEDIASVR-4-PARTITION_USAGE_ALERT : High disk usage alert : host /misc/scratch exceeded 87%
admin
run
ssh 10.0.2.16
ls /misc/scratch
...you will see lots of files...
...
default-sdr--1_core_2020-11-03-06:51_2_hbmiss
default-sdr--1_core_2020-11-03-06:53_2_hbmiss
default-sdr--1_core_2020-11-03-06:54_2_hbmiss
default-sdr--1_core_2020-11-03-06:55_2_hbmiss
default-sdr--1_core_2020-11-03-06:56_2_hbmiss
default-sdr--1_core_2020-11-03-07:19_2_hbmiss
default-sdr--1_core_2020-11-03-07:57_2_hbmiss
default-sdr--1_core_2020-11-03-08:14_2_hbmiss
...
cd /misc/scratch/
rm -rf *core_2020*
....look at the nice message that the /misc/scratch was at 87%...but now back to normal... 6%
Nov 4 17:42:33.504 UTC: mediasvr[2775]: %MEDIASVR-MEDIASVR-4-PARTITION_USAGE_NORMAL : Back to normal disk usage : host /misc/scratch below 6%