Re: [Non-DoD Source] Re: Slow initial resync in RAID6 with 36 SAS drives
flat view
From: antlists <hidden>
Date: 2021-09-01 01:22:30
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. It'd be nice to fix it, but retro-fitting existing code is a lot more work than starting from scratch ... Cheers, Wol