On Wed, Apr 1, 2015 at 2:57 PM, Wols Lists <antlists@xxxxxxxxxxxxxxx> wrote: > On 01/04/15 19:46, Alireza Haghdoost wrote: >>> Now, how can be assured, in that case, that the "cache" >>> > device is safe after the power is restored? >> You do sync write-ahead logging on the Flash cache. If it return >> successful, you do fire the writes to the RAID. If system crash/fails >> during the RAID writes (Write-hole), you just recover data by scanning >> write-ahead log in the flash cache and replay the logs into the RAID >> drives. >> > Just to throw something nasty into the mix, I'm not sure whether it's > SSDs or SD-cards, but there certainly *was* a spate of corrupted > *controllers*. > > In other words, a power failure would RELIABLY TRASH the device, if it > happened at the wrong moment. Hopefully that's been fixed ... > That is certainly true. As Dan mentioned, the cache device it-self should be safe against power failure. I agree this is not the case for all SSD cards in the market but might be the case for Facebook. I hate to say this but It seems these efforts are useful dependent to what kind of hardware is deployed for cache device. --Alireza -- 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
