On Tue, Aug 30, 2011 at 03:53:48PM +0100, Darren J Moffat wrote: > On 08/30/11 15:31, Edward Ned Harvey wrote: >>> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- >>> boun...@opensolaris.org] On Behalf Of Jesus Cea >>> >>> 1. Is the L2ARC data stored in the SSD checksummed?. If so, can I >>> expect that ZFS goes directly to the disk if the checksum is wrong?. >> >> Yup. > > Note the following is an implementation detail subject to change: > > It is NOT checksumed on disk only in memory, but the L2ARC data on disk > is not used after reboot anyway just now.
It's not checksummed on disk as a direct function of L2ARC storage with an L2ARC checksum because that's unnecessary - the cached data is verified against the original zfs checksums. And, yes, if it fails it counts as a "bad read" and zfs tries again from the data pool. It's checksummed on the way into memory, from either pool disk or l2arc disk. If it's already in ARC memory, it's just a hit and the checksum is not done each time - that would be ludicrously expensive, and is one of the ways non-ECC systems can corrupt data. L2ARC persistence may require adding checksumming to the L2ARC on-disk format, but presumably for the L2ARC metadata that will need to be stored persistently (and now only exists in ram), not so much for the cached pool data. -- Dan.
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