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Hard drive "efficiency" and how does WHS see RAID? RRS feed

  • Question

  • I asked these questions in a thread in the software forum but it looked to be to be too much of a derail from the original topic so I decided to ask here.  Sorry if this has been answered before, I can't find it if it has.  I have two questions, first is after the quote from cek:

     

     cek wrote:

    First some backgrounder information on how the Drive Extender storage system works.

    Windows Home Server, when initially installed on a machine, formats all internal disks.  On the first disk (we call this the primary disk) we create two partitions and format them with NTFS:

    C: (10GB) - used for the system
    D: (the rest) - the "Primary" data partition

    Subsequent disks are formated as one NTFS partition and are known as "secondary disks".

    The primary data partition (the second partition on the primary disk) is special because that is where Drive Extender starts working it's magic from. This is where all "tombstones" are stored. Tombstones are really NTFS reparse points that DE understands. They are tiny files that redirect to one or two "shadows".  The shadows are where your data really is, and shadows always exist on partitions other than the primary.  If duplication is on for a shared folder there will be 2 shadows. If duplication is off there will be 1.

     

     

    Reading your last paragraph raised a red flag with me.  If I have three 500GB drives and have duplication enabled, since the primary data partition contains only tombstones I'm only getting 500 GB worth of usable drive space with 1.5 TB of drives.

     

    My assumption from reading that is that I will only get 1/3 of the total capacity of three identical drives as actual storage room (if duplication is on).  Is this correct?

     

    Building further on the assumption above leads me to another question, one about RAID 5.

     

    Say for example I build my server with the three identical 500GB drives (because that's what's in my newegg shopping cart for my WHS build, but that's neither here nor there ) but instead of going the supported route of installing the OS on one drive, 10 Gig partition with the rest reserved for tombstones blah blah blah, I institute hardware RAID 5 via a PCI card with it's own BIOS.

     

    How does the OS partition and "see" the drives at this point since there is only one drive as far as the OS is concerned?  Does it partition the 10 Gig, use the balance of the 1 TB as "Tombstone room" and wait for additional drives to be added so it can actually store something?

     

    Again, sorry if this has already been answered somewhere and is common knowledge by now.  I've browsed these forums a lot in the last three or four days and haven't found answers to these specific questions.

    Tuesday, April 24, 2007 4:06 AM

All replies

  • No, with duplication on you will (eventually) get the full 1.5 TB of space used. WHS doesn't follow a simple rule regarding disk usage as far as I can tell. It tries to keep all files off the primary system drive, but that's for data integrity. If everything else fills up and the partition behind D: is all that's left, I'm sure it will use that space. Files in duplicated shares will use up 2x their actual size in your storage pool, though. You can see how much space duplication is using in the pie chart on the Storage tab in WHS Console.

    As for RAID, assuming you can configure your system to boot off of the RAID array, and assuming you can get WHS to load the drivers for it, then you should be able to install onto the RAID array, and WHS will see it as one large logical drive.
    Tuesday, April 24, 2007 12:18 PM
    Moderator
  •  Ken Warren wrote:
    No, with duplication on you will (eventually) get the full 1.5 TB of space used. WHS doesn't follow a simple rule regarding disk usage as far as I can tell. It tries to keep all files off the primary system drive, but that's for data integrity. If everything else fills up and the partition behind D: is all that's left, I'm sure it will use that space. Files in duplicated shares will use up 2x their actual size in your storage pool, though. You can see how much space duplication is using in the pie chart on the Storage tab in WHS Console.

    As for RAID, assuming you can configure your system to boot off of the RAID array, and assuming you can get WHS to load the drivers for it, then you should be able to install onto the RAID array, and WHS will see it as one large logical drive.

     

    Yeah I'm not so sure about your first paragraph, I think the person I quoted above (cek) may be a Microsoft employee, not sure though.  Anyway he said this:

     

    The primary data partition (the second partition on the primary disk) is special because that is where Drive Extender starts working it's magic from. This is where all "tombstones" are stored. Tombstones are really NTFS reparse points that DE understands. They are tiny files that redirect to one or two "shadows".  The shadows are where your data really is, and shadows always exist on partitions other than the primary.

     

    To me this isn't a huge problem as I probably will run duplication on my pictures folder only, and maybe some financial type files also so it won't be a big storage hit.  Someone that duplicates everything could see their actual storage be much smaller than their perceived storage.  It's an interesting discussion until we hear something from the horses mouth.

     

    As far as the RAID goes, I'm a newby so I'm asking more as a proof of concept than anything else.  I'm picturing WHS with duplication turned off installed on a hardware RAID5 array (with all the "if's" going right, humor me) on the normal 10 GB partition.  Can you then partition a second portion of the array to act as the primary data partion that will hold all the tombstones?

     

    Is this feasable and if so, does it combine the ease of use of WHS with the redundancy of RAID5 to the point of not worrying about losing even the OS partition should one drive fail?

    Wednesday, April 25, 2007 5:23 AM
  • Yes, Charlie works for Microsoft. He heads up the WHS team.

    And I'm also pretty sure about my first sentence. If you have only one disk in WHS, it contains everything. If you add a second disk, the first disk (the primary data partition, D: ) contains tombstones and share duplications. I've observed both of those conditions. Add a third drive and duplication moves off the primary data partition too. I've also observed that.

    I have too much storage in my WHS now to easily test the third condition, but I would expect that filling up your secondary storage drives would put data back on the primary drive. I'm pretty certain that Charlie was talking about the case of a WHS system with plenty of free storage, not one that's almost full.

    RAID: assuming you can get your system to boot off your RAID array, and more importantly get it to present that array to WHS as disk 0 at installation, WHS will take the first 10 GB as SYS (C: ) and the rest as DATA (D: ). You don't have any control over that process, though, beyond configuring your hardware correctly and supplying drivers at the right times. WHS does the partitioning.
    Wednesday, April 25, 2007 12:07 PM
    Moderator