On 5/20/2011 3:24 PM, Drew wrote: >> It's a shame; maybe there will be disks with battery-backed cache >> one day. > > There's already hybrid drives which pack a small SSD onboard to act as > a large cache. These hybrid drives still have a small 32-64MB cache DRAM, in front of the SSD. The DRAM loses its contents when the power goes out. The on board SSD doesn't prevent this cache data loss. It may be worth noting that most, if not all, pure SSDs also have cache DRAM in front of the flash array, and thus will lose data in the cache when the power fails. Some models have what has been termed "super capacitors" on board to power the device long enough to flush pending writes in cache to the flash cells, but few, if any, of the manufacturers advertise that their drives have this feature, or even bother to put it on the spec sheet. So there's no easy/consistent way, at present, to really know if your SSD has this feature or not. As always, a good data persistence strategy starts with a good UPS. Laptop users have an advantage as they get a free built in UPS, and typically, good software integration to automatically and safely shutdown when the battery is about out of juice. -- Stan -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
