On Thu, Oct 13 2016, Song Liu wrote: > This is the recovery part of raid5-cache. > > With cache feature, there are 2 different scenarios of recovery: > 1. Data-Parity stripe: a stripe with complete parity in journal. > 2. Data-Only stripe: a stripe with only data in journal (or partial > parity). > > The code differentiate Data-Parity stripe from Data-Only stripe with > flag (STRIPE_R5C_WRITTEN). > > For Data-Parity stripes, we use the same procedure as raid5 journal, > where all the data and parity are replayed to the RAID devices. > > For Data-Only strips, we need to finish complete calculate parity and > finish the full reconstruct write or RMW write. For simplicity, in > the recovery, we load the stripe to stripe cache. Once the array is > started, the stripe cache state machine will handle these stripes > through normal write path. > > r5c_recovery_flush_log contains the main procedure of recovery. The > recovery code first scans through the journal and loads data to > stripe cache. The code keeps tracks of all these stripes in a list > (use sh->lru and ctx->cached_list), stripes in the list are > organized in the order of its first appearance on the journal. > During the scan, the recovery code assesses each stripe as > Data-Parity or Data-Only. > > During scan, the array may run out of stripe cache. In these cases, > the recovery code will also call raid5_set_cache_size to increase > stripe cache size. What if this fails. Maybe the array was created on a machine with lots or memory, but that machine died and you are trying to recovery you data on a much less capable machine. I don't think there is an easy answer, but at least you need to fail gracefully. I'll try to look at the rest tomorrow. NeilBrown
Attachment:
signature.asc
Description: PGP signature
