Hi there. I've come across this board a few times googling for answers regarding intel controllers. Very interesting stuff I've found here. So, to the point, I have two computers. Home and work.

Mainboards are Asus P9X79-E WS(intel C600 series) and Asrock Z97 Pro4(intel 9 series). Both Windows 8.1 machines with Vmware Workstation on them. Both with internal mechanical system drives and external bays to swap storage drives so I can carry my work wherever I go.

For that, as a portable storage drive, I'm using a Samsung SSD 840 Pro 256. On that drive I have a Vmware Workstation virtual machine disk drive file(vmdk). The idea is to save some money on software licenses that I have installed on my virtual machine since remote desktops or laptops do not suit my needs.

It was working well up until I decided to test the intel RST drivers performance on the z97. The x79 at home was left with the MS AHCI standard because the C600 series is not supported in the last RST drivers package.

Then I left work to go home. Put my SSD drive into the external drive bay slot and the virtual machine would not boot. The vmdk file properties on the SSD was 0 bytes in size.

The next morning I went to work and the vmdk file was again 100gb or so and the virtual machine was working just fine. A weird glitch I thought. But no. Later on, at home it was 0 bytes again.

I tried copying the entire file again from backup but whenever I did file changes on one computer it was showing inconsistencies on the other(unindexed files found with chkdsk utility).

The solution was to force the same RST driver on the x79 with the RST floppy package. The old RSTe package from Asus supports the C600 series but it didn't do the trick. It's all good now but my question remains. Why?

Can someone shed some light?

I would like to add that the z97 system partition is GPT as well as the portable SSD. And the system partition on the x79 is MBR. It was the same prior changing drivers. Could it be that recent versions of RST drivers handle the partition file contents differently? Like changing the table of contents location or something like that?

Thanks. I'm looking forward to your insight. As it turns out I spoke too soon. I'm still having inconsistencies. To me it seems as if the z97 is reading the GPT backup partition table from the SSD. Maybe the main table is being corrupted with random writes every now and then. Because I can tell that sometimes the files copied on the SSD at home are missing later on at work. And the only files left are the exact same ones that were there the last time I left work. It does not always happen but I can tell there's a pattern. It could be a problem with GPT partitioning on my Samsung SSD but it was working fine under MS AHCI drivers (at least I think it did because right now I'm starting to doubt myself). And that never happens while staying at one place. I guess I'll have to rollback for now...

Oops. That post above was me. I must have had an old forgotten user credentials saved. As I said before I've been a lurker around here. Merry Christmas everyone btw.

Ok. I'm now on MS AHCI standard driver on both computers. No corruption so far. Looking around, I've found this old thread:
http://forums.anandtech.com/showthread.php?t=2228064

It was helpful to pin down the cause of my symptoms more accurately. They used gptfdisk utility to check the GPT partition. So I did. As I suspected, every time I change computers, random data is being written over the backup GPT partition.
They recommend to stick to MBR. At least for Samsung SSDs. That thread is more than two years old and my Samsung firmware is up to date. So I don't think that issue is going to be fixed anytime soon. I don't know if the RST drivers are the culprit here but now that I'm back on MS AHCI the issue seems to be gone.
I'd rather stay on GPT and MS AHCI instead of MBR because theoretically GPT is more robust and there's not much of a performance gain between MS AHCI and intel RST drivers anyway. I'd be nice, though, to know why this is happening and what does the RST driver do differently to cause this.

Update: Still on MS AHCI. I'm running chkdsk and gptfdisk every time I swap the drive for the time being. Just to be sure. And chkdsk always end up doing some minor changes. Security descriptors and index entries. No corruption but not a good sign either. I'm going to give it some more over provisioning space with Samsung Magician to see if that helps. Otherwise I might be better off with MBR after all.

It's been a few days now. Switching to MBR didn't solve the problem. I'm posting back here because I finally found the solution. Wasn't firmware or driver related as it turns out. It was the Windows 8 Fast Boot feature. During fast boot the system loads the hiberfile and does not use the files on the filesystem. The hibernation maintains the file structure so if you try to save a file into the external drive from one computer it will get lost on the other as it only remembers the old file structure. And that's the recipe for data loss. So, there you go, disable Fast boot if you are experiencing such behaviour. Now I'm happily back on GPT and Intel RST. No issues at all.

Edit: and just to clarify things so it makes sense from the start, the reason it was working well before changing drivers was because, to test the new driver performance, I fiddled with Samsung Magician OS Optimization settings thus enabling hibernation (and fast boot) unintentionally. That's why I thought it was a driver issue.