My G RAID thunderbolt drive mounted just fine onto my iMac this morning. And now it will not mount despite my various efforts. I don't know what else to do. Can someone help me with this?

My G RAID thunderbolt drive mounted just fine onto my iMac this morning. I copied some files from another drive onto the RAID drive, ejected it, and worked on another project for a few hours. When I went to mount the RAID drive again so I could work on the project associated with the drive (I'm a freelance video editor) it would not mount. I've tried everything. It boots up perfectly fine, the drive seems to have no hardware problems. It shows up on Disk Utility and in System Information but is listed as not mounted. I've verified it on Disk Utility and it tells me everything with the drive is fine. I've tried all the various restarting my iMac, ejecting and reconnecting the drive, shutting down the whole system and starting it back up, relaunching Finder, and nothing works. Starting to panic because this is a client's drive, I have no idea what the issue is, it worked perfectly fine only hours ago, nothing happened to it in the meantime, and I fear continuously connecting and ejecting it because I don't know what the state is with the data and if this is only going to further aggravate the problem. I've been up and down Apple and g-raid forums and can't get a straight answer anywhere. I need to know that the data is safe, the drive is undamaged, and how to get it to mount on my iMac. Can anyone out there help me with this??