The sg driver is used for scsi devices like tape, CD etc. The kernel panic occurs when memory of size 2K is allocated more thant 20 times by the sg driver. Yosemite backup software with RHEL-5 will result in this hang. This can be induced by a utility to read/write 2k buffers 20 times.

If direct i/o is done with tape drives using commands like tar in fixed block mode with buffer sizes that are not a multiple of the already formatted tape's block size then a call trace and system hang can be observed. The issue is not specific to any HBA and is more easily reproducible with reads

...DR Series system contains data backup and management software preinstalled...encryption in the backup software, you will...DR Series system considers...Controller • Software – Operating System – Supported Backup Software...