Overlay is earlyboot feature which allows to overlay cloudboot image with any customised hardware drivers to be executed before the IS service is started.
Please note that this doesn't apply cleanly to NIC drivers though the NIC drivers have to load first in order to access the CP NFS resource. So they are embedded in the cloudboot ramdisk image.
ISchecker is able to detect these customizations (thanks to Boris for it).
All customization files are stored on CP server. You can find them following the next path: /tftpboot/images/centosx/diskless/snapshot/hv_mac_addr_dir/overlay/.
For example: /tftpboot/images/centos5/diskless/snapshot/90-e2-ba-73-8a-00/overlay/
When you moving out these files (because of occurring failures in starting IS daemons) please test them by reapplying on one of HVs one by one as long as they may contain important customization which is needed for appropriate work of storage network; benchmarks etc. It will allow to determine which files are problematic towards IS functionality.
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