Sounds good but also completely unrelated. You should really post a new thread for this and not using the request function mode support topic. On 18.06.2014 15:57, Roberto Spadim wrote: > Just a comment about the read balance: > i'm talking about a /sys/block/mdX/queue/read_balance > today we have 'near head', we can do some read balances like freebsd, > but that's what i'm thinking about: > cat /sys/block/mdX/queue/read_balance: > [nearhead] roundrobin timebased stripe > > ------------ > NEARHEAD: > today read balance, each write/read, mark the position of disk > 'head', sequencial reads are done by the same disk, non sequencial > reads select the disk with min(current position - read position) value > here i'm thinking about debugging, we could implement some sys files > > cat /sys/block/mdX/queue/nearhead_info: > > /dev/sda1 (device 1) - current position: xxxx > /dev/sda2 (device 2) - current position: xxxx > /dev/sda3 (device 3) - current position: xxxx > ... > > > ------------ > ROUNDROBIN: > select the disk based on reads/disk, current disk and current disk > reads, here some configurations: > > cat /sys/block/mdX/queue/roundrobin_info > > /dev/sda1 (device 1) - reads count: xxxxx, max reads: yyyyy, current disk > /dev/sda2 (device 2) - max reads: yyyyy > /dev/sda3 (device 3) - max reads: yyyyy > > MAX READ VARIABLE: > cat /sys/block/mdX/queue/roundrobin_maxreads_dev1 > yyyyy > echo 1234 > /sys/block/mdX/queue/roundrobin_maxreads_dev1 > cat /sys/block/mdX/queue/roundrobin_maxreads_dev1 > 1234 > > READ COUNT VARIABLE: > cat /sys/block/mdX/queue/roundrobin_readcount_dev1 > xxxxx > echo 1234 > /sys/block/mdX/queue/roundrobin_readcount_dev1 > cat /sys/block/mdX/queue/roundrobin_readcount_dev1 > 1234 > > CURRENT DISK VARIABLE > cat /sys/block/mdX/queue/roundrobin_currentdevice > xxxxx > echo 1 > /sys/block/mdX/queue/roundrobin_currentdevice > cat /sys/block/mdX/queue/roundrobin_readcount_dev1 > 1 > > > ---------------- > STRIPE: > it's something like raid0, each disk read one part of the array > > /sys/block/mdX/queue/stripe_array_shift > this one, select how many bytes/sectors, per disk, for exaple, from > 0-100 disk 1, 101-200 disk 2, 201-300 disk 3, 301-400 disk 1, 401-500 > disk 2 .... etc, that's just a number of how many sectors/bytes per > disk > > > --------------- > TIME BASED: > this one, is more specific per disk, and we can mix ssd and hdd, it's > just a standard model and can change, but it give 1% of speed up with > ssd+hdd arrays > > the expected time to read is: > (read_rate_sequencial * read_size) + > (head_distance_rate * head_distance) + > fixed_access_time_non_sequencial + > fixed_access_time_sequencial + > queue_expected_time > > a example for hd: > read_rate_sequencial = 180mb/s (must invert since we need s/mb) > head_distance_rate = 10ms/total_disk_size > fixed_access_time_nonsequencial = ~10ms (1 disk rotation, this can be > disk rpm => 7200rpm = 120hz, 1/120 = 0.008333 seconds) > fixed_access_time_sequencial = 0 > queue_expected_time = (must check queue if we could get this information) > > for ssd: > read_rate_sequencial = 270mb/s > head_distance_rate = 0 > fixed_access_time_sequencial = 0,1ms (ocz vertex 2 ) > fixed_access_time_non_sequencial = 0,1ms (ocz vertex 2 ) > > > examples with 20MB, considering disk at current position: > hd: > (0.0055555 * 20) + (180mb/s = 0.00555s/mb) > (0.000009765625 * 0) + (considering 1tb disk => 10ms/1024gb, > 10ms/1024000mb = 0.000009765625mb/ms) > 0 + > 0 > =0.11111 second, (just mb/s matters here) > > > ssd: > (0.0037037037037037 * 20) + (270mb/s = 0.0037037037037037s/mb) > (0 * 0) + (0ms / total ssd size = 0) > 0,0001 (0,1ms) > = 0.0740 second (mb/s + access time of 0,0001second) > > > for small reads, this model select hd when it's near head position, > for bigger reads it select ssd, if we could consider queue of ssd and > hdd, we have a better read time prediction, it does a nice work (1% of > speedup) but have many parameters / disk > > ------- > there's an old implementation at raid1.c here: > http://www.spadim.com.br/raid1/raid1.c > -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
