Raidz1 or z2? One of the reasons I went with z2 is because of the “raid5 is dead” thing, argument basically being, drives are so large that if 1 fails, you are statistically almost guaranteed to encounter a read error during the rebuild when you no longer have any redundancy, so double redundancy is a necessity nowadays.
Raidz5 doesn’t exist, I assume you mean raid5? And you wouldn’t know, URE is sometimes silent, and because without parity during a rebuild you would be recalculating the parity bit and assumig every read on the remaining drives is successful. Except the URE rate for drives hasn’t gone down to match the increasing size of drives - so for a full 1x read of a large drive, you’re statistically at risk to get at least 1 URE.
In short, there is no integrity checking when rebuilding a single redundancy array after a drive failure, so just because a rebuild succeeds, doesn’t mean nothing was lost or corrupted. With double redundancy, you will still have single redundancy during a rebuild, so you would be able to detect URE and retry reads or raise an error to the user.
Some articles may make it overblown - you won’t lose your whole array, but any files stored in the block that had the URE during rebuild would be lost. And you might not know that it happened.
I’ve seen a calculation somewhere for drive speed, size and scrub frequency where optimal number of extra drives was calculated. On fast storage and with weekly scrubs one extra drive should be mostly fine.
My philosophy is any raid is not really a data contingency solution - it just saves some time when the drive fails.
Raidz1 or z2? One of the reasons I went with z2 is because of the “raid5 is dead” thing, argument basically being, drives are so large that if 1 fails, you are statistically almost guaranteed to encounter a read error during the rebuild when you no longer have any redundancy, so double redundancy is a necessity nowadays.
I have a raidz5 array of 8tb drives, one died, replaced it with no issues
Raidz5 doesn’t exist, I assume you mean raid5? And you wouldn’t know, URE is sometimes silent, and because without parity during a rebuild you would be recalculating the parity bit and assumig every read on the remaining drives is successful. Except the URE rate for drives hasn’t gone down to match the increasing size of drives - so for a full 1x read of a large drive, you’re statistically at risk to get at least 1 URE.
In short, there is no integrity checking when rebuilding a single redundancy array after a drive failure, so just because a rebuild succeeds, doesn’t mean nothing was lost or corrupted. With double redundancy, you will still have single redundancy during a rebuild, so you would be able to detect URE and retry reads or raise an error to the user.
Some articles may make it overblown - you won’t lose your whole array, but any files stored in the block that had the URE during rebuild would be lost. And you might not know that it happened.
You can read about it here: https://www.servnetuk.com/insights/ure-is-raid-5-dead
I’ve seen a calculation somewhere for drive speed, size and scrub frequency where optimal number of extra drives was calculated. On fast storage and with weekly scrubs one extra drive should be mostly fine.
My philosophy is any raid is not really a data contingency solution - it just saves some time when the drive fails.