Ellis, Mike wrote:
Also the "unmirrored memory" for the rest of the system has ECC and ChipKill, which provides at least SOME protection against random bit-flips.
CF devices, at least the ones we'd be interested in, do have ECC as well as spare sectors and write verification. Note: flash memories do not suffer from the same radiation-based bit-flip mechanisms as DRAMS or SRAMS. The main failure mode we worry about is write endurance.
Question: It appears that CF and friends would make a descent live-boot (but don't run on me like I'm a disk) type of boot-media due to the limited write/re-write limitations of flash-media. (at least the non-exotic type of flash-media)
Where we see current use is for boot devices, which have the expectation of read-mostly workloads. The devices also implement wear leveling.
Would something like future zfs-booting on a pair of CF-devices reduce/lift that limitation? (does the COW nature of ZFS automatically spread WRITES across the entire CF device?) [[ is tmp-fs/swap going to remain a problem till zfs-swap adds some COW leveling to the swap-area? ]]
The belief is that COW file systems which implement checksums and data redundancy (eg, ZFS and the ZFS copies option) will be redundant over CF's ECC and wear leveling *at the block level.* We believe ZFS will excel in this area, but has limited bootability today. This will become more interesting over time, especially when ZFS boot is ubiquitous. As for swap, it is a good idea if you are sized such that you don't need to physically use swap. Most servers today are in this category. Actually, most servers today have much more memory than would fit in a reasonably priced CF, so it might be a good idea to swap elsewhere. In other words, it is more difficult to build the (technical) case for redundant CFs for boot than it is for disk drives. Real data would be greatly appreciated. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
