On 9/1/21 9:22 AM, antlists wrote:
On 25/08/2021 11:28, Finlayson, James M CIV (USA) wrote:
I'm not a person necessarily in the "know", but I mess with these in
udev for SSDs:
SUBSYSTEM=="block", ACTION=="add|change", KERNEL=="md*",
ATTR{md/sync_speed_max}="2000000",ATTR{md/group_thread_cnt}="64",
ATTR{md/stripe_cache_size}="8192"
Guidance on why I change the values this way - educated "guess", as
I'm an experienced practitioner at best and not someone that messes
with the code......I've seen resync rates as high as 900MB/s
sustained on my SSD mdraids, even though the SSDs should be able to
sustain higher.....
Not raid, but I've picked up on comments (on LWN?) that certain
file-systems are very much "single threaded" in their behaviour. I
strongly suspect that md-raid predates common multi-cpu/multi-core
systems, and I've heard somewhere that md-raid doesn't thread that well.
Yes and no, raid5 does support multi-threading if group_thread_cnt > 0,
but IIUC, only one thread (mdx_resync) deals with resync IO.
Thanks,
Guoqing
