So, I'm currently experiencing an issue with my FreeNAS box using a huge iSCSI device extent (outlined here -- http://forums.freenas.org/showthread.php?7448-Hanging-on-boot-import)
The crux of the issue seems to be that, in addition to 2 out of my 6 x 2Tb drives dedicated to RAID-Z2 redundancy information, the ZFS Volume I created to hold the iSCSI target also needs at least 100% of its own size for 'metadata'
E.g. I create a non-sparse ZFS Volume of 6Tb on a 7.1Tb pool - leaving 1.1Tb of free space available. The 6Tb is then handed off to iSCSI as a block device (so that Windows can attach and format it as NTFS).
My understanding was that the Volume would be fixed at 6Tb.
However, windows gets as far as copying roughly 3.5Tb over to the iSCSI device, and I run out of space on the parent pool.
It would appear that the ZFS Volume (while fixed at 6Tb) requires additional space for 'metadata' as the volume is used up. This would appear to support many of the documents I found which said that 'metadata' was not allocated at volume creation time, and instead is allocated on demand.
Now, what I don't understand is (and I've been unable to find any real explanation)...
a) what the hell is metadata
b) why does a block device like an iSCSI extent require metadata
Is this a bug in the volume creation? I found this bug (from a link supplied by paleoN) which smells a bit suspicious -- https://www.illumos.org/issues/437
Can any of you ZFS experts explain the function of metadata to me (in idiots terms)?
Thanks
The crux of the issue seems to be that, in addition to 2 out of my 6 x 2Tb drives dedicated to RAID-Z2 redundancy information, the ZFS Volume I created to hold the iSCSI target also needs at least 100% of its own size for 'metadata'
E.g. I create a non-sparse ZFS Volume of 6Tb on a 7.1Tb pool - leaving 1.1Tb of free space available. The 6Tb is then handed off to iSCSI as a block device (so that Windows can attach and format it as NTFS).
My understanding was that the Volume would be fixed at 6Tb.
However, windows gets as far as copying roughly 3.5Tb over to the iSCSI device, and I run out of space on the parent pool.
It would appear that the ZFS Volume (while fixed at 6Tb) requires additional space for 'metadata' as the volume is used up. This would appear to support many of the documents I found which said that 'metadata' was not allocated at volume creation time, and instead is allocated on demand.
Now, what I don't understand is (and I've been unable to find any real explanation)...
a) what the hell is metadata
b) why does a block device like an iSCSI extent require metadata
Is this a bug in the volume creation? I found this bug (from a link supplied by paleoN) which smells a bit suspicious -- https://www.illumos.org/issues/437
Can any of you ZFS experts explain the function of metadata to me (in idiots terms)?
Thanks