Please excuse my pitiful example. :-) I meant to say "*less* overlap between virtual machines", as clearly block "AABB" occurs in both.
-----Original Message----- From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-boun...@opensolaris.org] On Behalf Of Chris Murray Sent: 18 March 2010 18:45 To: zfs-discuss@opensolaris.org Subject: [zfs-discuss] Validating alignment of NTFS/VMDK/ZFS blocks Good evening, I understand that NTFS & VMDK do not relate to Solaris or ZFS, but I was wondering if anyone has any experience of checking the alignment of data blocks through that stack? I have a VMware ESX 4.0 host using storage presented over NFS from ZFS filesystems (recordsize 4KB). Within virtual machine VMDK files, I have formatted NTFS filesystems, block size 4KB. Dedup is turned on. When I run ZDB -DD, i see a figure of unique blocks which is higher than I expect, which makes me wonder whether any given 4KB in the NTFS filesystem is perfectly aligned with a 4KB block in ZFS? e.g. consider two virtual machines sharing lots of the same blocks. Assuming there /is/ a misalignment between NTFS & VMDK/VMDK & ZFS, if they're not in the same order within NTFS, they don't align, and will actually produce different blocks in ZFS: VM1 NTFS 1---2---3--- AAAABBBBCCCC AAAABBBBCCCC ZFS 1---2---3---4--- ZFS blocks are " AA", "AABB" and so on ... Then in another virtual machine, the blocks are in a different order: VM2 NTFS 1---2---3--- CCCCAAAABBBB CCCCAAAABBBB ZFS 1---2---3---4--- ZFS blocks for this VM would be " CC", "CCAA", "AABB" etc. So, no overlap between virtual machines, and no benefit from dedup. I may have it wrong, and there are indeed 30,785,627 unique blocks in my setup, but if there's a mechanism for checking alignment, I'd find that very helpful. Thanks, Chris -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
