On Thursday April 9, steven@xxxxxxxxxxxxxxx wrote: > Given I have a pair of 1TB drives Raid1 I'd prefer to reduce any recovery > sync time. Would an internal bitmap help dramatically, and are there any > other benefits. Bryan answered some of this but... - if your machine crashes, then resync will be much faster if you have a bitmap. - If one drive becomes disconnected, and then can be reconnected, recovery will be much faster. - if one drive fails and has to be replaced, a bitmap makes no difference(*). - there might be performance hit - it is very dependant on your workload. - You can add or remove a bitmap at any time, so you can try to measure the impact on your particular workload fairly easily. (*) I've been wondering about adding another bitmap which would record which sections of the array have valid data. Initially nothing would be valid and so wouldn't need recovery. Every time we write to a new section we add that section to the 'valid' sections and make sure that section is in-sync. When a device was replaced, we would only need to recover the parts of the array that are known to be invalid. As filesystem start using the new "invalidate" command for block devices, we could clear bits for sections that the filesystem says are not needed any more... But currently it is just a vague idea. NeilBrown -- 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
