I have implemented a virtual block device in Linux that transparently compresses and decompresses data. In my implementation, the unit of compression is 4K. Multiple variable-size compressed blocks are stored in the same physical block, which in principle requires a read-modify-write sequence.
In contrast, NTFS compresses multiples of blocks (typically 64K clusters) and uses fewer 4K physical blocks (i.e. 32K) to store the compressed cluster. This approach eliminates the read-modify-write sequence but is less efficient for applications that exhibit small read/writes, as additional (and useless) decompressions/compressions are performed. I've been told that the ZFS file-system block ranges from 512 to 128K. Suppose that the ZFS file-system block is 4K or less and that the physical block is 4K (not 512). Compressing 4K typically results in a 1K to 3K block. How does ZFS store segments of data that are smaller than the physical block? I need this information for a journal I am preparing for ACM's Transactions on Storage (an extended work of two papers), as I want to compare my system to NTFS and ZFS. -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
