• Raid Controller: 3Ware 9650SE-24M8
  • Disks: 21 x 1TB RAID5
  • Stripe 64KB


  • OS: Windows Server 2003 SP2 32x
  • Disk: Dynamic 19557.44GB
  • Volume: Capacity 15832.19GB

I guess my array must have a 4KB block size which is limiting it to 16TB. I think I would have to switch to a 64KB block size to be able to see a maximum of 256TB. Or create another unit on my controller to go above 16TB of storage.

Unfortunately I have already added over 16TB, ideally I would like to shrink the array and reclaim the 5 disks that aren't doing anything. I don't think this is possible. More likely, can I change the block size so 20TB becomes visible in windows?


My problem is the array has accepted over 16TB of disks but isn't displaying it. I can see no way to reclaim the disks without destroying the array or changing the cluster size. I'm concerned changing the cluster size might take days/weeks/months? using Acronis. I've opted to purchase four 3TB drives to migrate the data off and then I'll rebuild the array as two smaller volumes. Thanks for your help :)

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    Yeah, sounds like you've got a 4kb cluster size; verify with fsutil fsinfo ntfsinfo. Do you already have data on this volume? I'm not aware of any way to change the size other than a reformat. – Shane Madden Nov 22 '11 at 17:24
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    Yup, 4096 byte clusters * 2^32 cluster max = 16 TB. Can you reformat? – Shane Madden Nov 22 '11 at 17:50
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    DO NOT USE RAID 5 for a 21 disk array of 1TB disks. You will have Unrecoverable Read Errors on Rebuild. – Tom O'Connor Jan 5 '12 at 14:25
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    I know you won't want to hear this but a 21 disk RAID5 array is wildly irresponsible, most disk controllers won't even let you create one this size. I'm surprised it works properly at all and your rebuild window will be so large that the risk of losing a second disk during this period, and thus losing all your data, is way too large. This WILL fail and you'll have wished you'd gone with RAID 6. Just saying. – Chopper3 Jan 5 '12 at 14:26
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    I'd probably go with RAID 60 or something nesty. – Tom O'Connor Jan 5 '12 at 14:29

16TiB is the maximum volume size with 4K clusters.

You'll need to do one of:

  • reformat with a larger cluster size
  • change the cluster size to 8K (apparently Acronis can do so)
  • create another NTFS volume so you can use that unallocated space. You can then mount that volume onto a folder in your C drive if you prefer having a single drive, but you'll have to remember you still have the 16TB/5TB restriction. (thx for the suggestion 'Multiverse IT')
  • One suggestion related to this would be to use an NTFS Junction - depending on your folder structure, you may be able to put 5 TB of data (give or take) into a separate volume and then mount that volume on the 16 TB volume so that it LOOKS like it's all on one. This would be cheaper than Acronis and less time consuming than a backup reformat, and restore. – Multiverse IT Nov 27 '11 at 5:14

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