On Mon, Nov 4, 2019 at 4:33 PM Wols Lists <antlists@xxxxxxxxxxxxxxx> wrote: > > On 04/11/19 20:01, Nigel Croxon wrote: > > The MD driver for level-456 should prevent re-reading read errors. > > > > For redundant raid it makes no sense to retry the operation: > > When one of the disks in the array hits a read error, that will > > cause a stall for the reading process: > > - either the read succeeds (e.g. after 4 seconds the HDD error > > strategy could read the sector) > > - or it fails after HDD imposed timeout (w/TLER, e.g. after 7 > > seconds (might be even longer) > > Okay, I'm being completely naive here, but what is going on? Are you > saying that if we hit a read error, we just carry on, ignore it, and > calculate the missing block from parity? > > If so, what happens if we hit two errors on a raid-5, or 3 on a raid-6, > or whatever ... :-) Based on my understanding (no data on this), the drive will retry read internally before return error. Therefore, host level retry doesn't really help. But I could be wrong. Song
