In case of RAID1 and RAID10 devices are mirror-ed, a read IO can pick any device for reading. This choice of picking a device for reading should be configurable. In short not one policy would satisfy all types of workload and configs.
So before we add more policies, this patch-set makes existing $pid policy configurable from the mount option and adds a devid based read_mirror device policy. And keeps $pid based policy as the default option for now. So this mount option helps to try out different read mirror load balances. Further we can add more policies on top of it, for example.. mount -o read_mirror_policy=pid (current, default) [1] mount -o read_mirror_policy=<devid> [2] mount -o read_mirror_policy=lba (illustration only) [3] mount -o read_mirror_policy=ssd (illustration only) [4] mount -o read_mirror_policy=io (illustration only) [5] mount -o read_mirror_policy=<heuristic1> (illustration only) [6] [1] Current PID based read mirror balance. [2] Set the devid of the device which should be used for read. That means all the normal read will go to that particular device only. This also helps testing and gives a better control for the test scripts including mount context reads. [3] In case of SAN storage, some storage prefers that host access the LUN based on the LBA so that there won't be duplications of caching on the storage. [4] In case of mix of SSD and HD we may want to use SSD as the primary read device. [5] If storage caching is not the bottleneck but the transport layer is then read load should be tuned based on the IO load. [6] Or a combination of any of above as per the priority. Timofey should consider to base his patch on top of this. Btrfs: enchanse raid1/10 balance heuristic This patch set is on top of the preparatory patch set: [PATCH 0/2] Preparatory to add read_mirror mount option Anand Jain (2): btrfs: add mount option read_mirror_policy btrfs: add read_mirror_policy parameter devid fs/btrfs/ctree.h | 2 ++ fs/btrfs/super.c | 31 +++++++++++++++++++++++++++++++ fs/btrfs/volumes.c | 18 +++++++++++++++++- fs/btrfs/volumes.h | 7 +++++++ 4 files changed, 57 insertions(+), 1 deletion(-) -- 2.7.0 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html