> [ ... ] - needed volume size is 60TB I wonder how long that takes to 'scrub', 'balance', 'check', 'subvolume delete', 'find', etc. > [ ... ] 4x HW Raid 5 with 1GB controller memory of 4TB 3,5" > devices and using btrfs as raid 0 for data and metadata on top > of those 4 raid 5. [ ... ] the write speed is not as good as > i would like - especially for random 8k-16k I/O. [ ... ] Also I noticed that the rain is wet and cold - especially if one walks around for a few hours in a t-shirt, shorts and sandals. :-) > My current idea is to use a pcie flash card with bcache on top > of each raid 5. Is this something which makes sense to speed > up the write speed. Well 'bcache' in the role of write buffer allegedly helps turning unaligned writes into aligned writes, so might help, but I wonder how effective that will be in this case, plus it won't turn low random IOPS-per-TB 4TB devices into high ones. Anyhow if they are battery-backed the 1GB of HW HBA cache/buffer should do exactly that, excep that again in this case that is rather optimistic. But this reminds me of the common story: "Doctor, if I stab repeatedly my hand with a fork it hurts a lot, how to fix that?" "Don't do it". :-) PS Random writes of 8-16KiB over 60TB might seem like storing small records/images in small files. That would be "brave". On a 60TB RAID50 of 20x 4TB disk drives that might mean around 5-10MB/s of random small writes, including both data and metadata. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
