So then of what use is the parity? And how is the metadata used to reconstruct bad data? I understand obviously what the metadata contains but I don't get how ZFS traverses through a file system and USES the metadata to construct bad blocks.
I understand that you write everything to separate blocks. My question was this: If you have initially two stripes over two disks like this: Disk 1: XXXX (Stripe Unit 1) Disk 2: XXXX (Stripe Unit 2) You then want to modify something in the first stripe unit with modifications which are smaller so now Disk 1 and Disk 2 stripes look like this: Disk 1: XXYY (the y's indicate modified bits or bytes or whatever) Disk 2: XXXX So now, with a full-stripe write, you then make new blocks for both stripes and just copy the data over to the new blocks. Now, tell me if I am write with what happens on a full-stripe write: You read in Disk 1 and Disk 2 stripes in the file system cache. You then apply the modifications to the Disk 1 stripe within the cache. After this, you compute the parity within the cache and finally you write out both Disk 1 Stripe and Disk 2 stripe to new blocks. Since the modifications to the disk 1 stripe (the Ys) were smaller than the total stripe size, the new sector which will be written to will be of a smaller stripe size than the originals. Is this correct? -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
