So this topic has been nagging me for quite a while, simply because it doesn't make any sense. Drive Extender is a file system filter driver and manages all data written to the D:\shares and D:\folders on the server. This means that all file creations generated by the OS will go through Drive Extender, which creates the Tombstone on the system drive and decides on which disk to place the primary shadow copy (and secondary shadow copy if duplication is enabled).

So I did some snooping into the HP code and found out how they are creating the Mac backup files. The Mac client places a file into the \Mac share on the server in the Backup directory named "somename.req", whatever you want to call it. The Server has a process that watches that directory for these files, and when it finds one it reads out two values, the requested name of the file and the size it should be. It then accesses a method in HP.DiskUtils.dll that does the actual file creation. That is a native dll, so I ran the Unix "strings" command on it, and saw that it appears they are using NtCreateFile which is a Win32 API call.

Instead of spending a lot of time testing with a Mac client, I circumvented that part by manually creating a "bigfile.req" with the contents "bigfile.macbackup 300000000000" which would be roughly 290GB. My server has a 1.5TB system drive with ~600GB free, and two 500GB drives each with just over 300GB free. I chose the 290GB so that DE should be able to store the file on any drive on the server.

What I found was that the system immediately created the bigfile.macbackup, and closer investigation showed that it was stored on the 500GB drive that had the most free space, not on the system drive. This is exactly the way Drive Extender is supposed to behave.

In the screenshot you'll notice:
* D:\shares\Mac\Backup is the WHS Server Storage as presented to the user (the Tombstone), with no insight into where the file is actually stored.
* D:\DE\shares\Mac\Backup is the actual physical storage location on the D: partition of the system drive. This contains the 550GB backup file for my wife's Macbook, which was too large to create on the secondary 500GB drives in the server.
* C:\fs\1J4\DE\shares\Mac\Backup is one of the secondary 500GB drives and contains the bigfile.macbackup I had the HP software create. Note that C:\fs\ is a virtual view into the secondary drives managed by Drive Extender.

Now, with this investigation I don't intend to discount that there have been several users that have had problems creating backup files for their Macs. I hope that having further insight into how the Server works will allow us to all benefit and hopefully figure out how to help these users make the most of their MediaSmart Servers.

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Alex Kuretz
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Really? It just seems to be a share like any other so I don't know why it would be constrained to the system drive for space calculations.

//edit

Looks like Alex proved that in fact it does NOT require system drive space for this to work. There are legitimate reasons it could fail if trying to create an extremely large TM volume and not having enough contiguous space.

I've backed up 4 macs on my EX series boxes and not had an issue at all, but I have never created a backup volume bigger than 250GB.

Thanks for motivating me to do some further testing on my EX490 and Mac.
First off I want to say that the reason I was saying it goes to the system drive is based on the documentation that I had received about this feature back when the EX480 series offered this feature.

As mentioned, I did some further testing and disproved that part (about it using only the system drive).
It still needs contiguous space on a single physical hard drive for sure and I would like to add that DE does NOT move this file once it is created.


My tools for this were:
- An EX490 with a single 750GB drive installed (contains OS).
- A spare 750GB drive (blank)
- A Mac Mini
- A Windows 7 (simply to RDP into the server and look at diskmgmt)

My EX490 has about a week's worth of backups, about 200 media files and roughly 20GB of other random files. No addins installed.
I started on the Mac Mini by creating a 100GB backup. It worked.
I kept on deleting it and upping it until I reached about 200GB and then would no longer successfully create them.
I then added the blank 750GB drive to the unit's storage pool, kept duplication off.
On the Mac Mini I then created a 550GB backup drive, it worked.
RDP'd to the server and it showed that the file was actually on the hard drive I just added.
Deleted the backup file using the Mac and then tried to create one of 800GB to see if it would span it over 2 physical drives (although I was 99% sure it wouldn't).
It failed right away as expected.
Now that the drive is empty again (because the 800GB failed), I looked at how large the space is on my 2nd drive.
It showed 99% free, which amounted to 698.54GB
I was able to create one of 698GB which diskmgmt then showed 0% free, 549MB available.
When attempting to create one of 699GB, it failed right away saying that there isn't enough space.

My concensus is that I was wrong about it needing the system drive and I apologize to anyone whom I've told that to.
The Mac backup drive needs contiguous space on a single physical hard drive.

Now this does not rule out the inability to create backup drives due to other errors though!

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Mind me asking where this file is located on the server?

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Yeah, it's in C:\program files\Hewlett-Packard\MediaSmart Server\ on the server.

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Alex Kuretz
Remote Notification: Monitoring and alerting for your Home Server via email, Twitter, text message, RSS, push notifications, and on your Mac desktop
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Thanks

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It's also worth noting that while some users might find this behavior annoying, it makes perfect sense. The Time Machine file is what is referred to as a sparse bundle file. It's a single contiguous file designed to act as a container for Time Machine backups. For this reason it needs to be a single sequential file on one physical volume. Theoretically it is possible at some later time that this could be addressed through the use of ZFS, etc, although with Apple recently putting the kabosh on ZF support I wouldn't hold my breath.

So, bottom line is if you don't have enough contiguous space, the best thing you can do is turn off folder duplication for a couple of your large shares, then create the TM backup size you need (assuming there is now a disk with enough free space to do it) then turn folder duplication back on. This should sort things out as far as the system allocating space appropriately.

Or turn off the duplication, consolidate free space with Perfect Disk (defrag) and them create it...

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EX475, 2 GB, LE-1640
PC1: Vista-->W7 Ultimate/32, (D-Drive RAID-5 Array)
PC2: Lenovo Laptop, Win XP Home SP3
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Thankfully I came across this post because I was getting the same annoying behavior. To make things even worse, I recently added a 2TB drive which has some data already added to it, maybe around 200-300GB. When trying to create the backup file from the Mac utility I could see it being created on the shared folder and then all of a sudden it would be gone, deleted for whatever reason. So a couple of things, if it needed the contiguous space and also chose the drive with the most space, then why wasn't it working? Seemed odd. Anyway I followed Alex's steps to "manually" create the file by intercepting the unique id given by the HP MSS before it was deleted again and then just when ahead and created the file myself as per below:



Now I have the W8824AA7YJX.macbackup and W8824AA7YJX.ok files created on my Mac share. I had to format the drive (Mac OS Extended - Journaled) once it was mounted (which happened automatically), I chose the default format options and then renamed the disk from unnamed (I think) to Time Machine. I hooked up a network cable to the Mac and then started with the initial Time Machine backup. Took about 1-2 hours I think for the 200GB and now it's working perfectly. I have been adding, deleting, restoring for the part few days and it's working without any issues. I was almost surprised at how easy this was to do.

Thanks Alex for the input, and hopefully this is another success story of a what I see as a failed feature that doesn't work correctly for people who decide to add a Time Machine backup AFTER adding data to the HP MSS. I can confirm however I was able to add a Time Machine backup the day my EX485 arrived. That was many months ago.

Glad to hear that helped, thanks for sharing your experience.

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Alex Kuretz
Remote Notification: Monitoring and alerting for your Home Server via email, Twitter, text message, RSS, push notifications, and on your Mac desktop
Have you tried our Add-Ins?