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Disk Latency
(and Other Random Numbers)
@AlTobey
Open Source Mechanic
Datastax
Disclaimer
This study is not strictly scientific.
- Drive diversity
- Run Time
- Time limitations
- Hardware Limitations (PCIe lanes, controllers)
Performance Potential
- micro benchmarks show what the hw/sw *can* do
- NOT what it will do
- what it will do is almost never as much as it can
- this is OK
The Art of Discovering and Choosing Tradeoffs.
A.K.A. Tuning & Benchmarking
cd /sys/block/sda/queue
cat rotational
echo 1 |sudo tee nomerges
echo 0 |sudo tee read_ahead_kb
echo noop |sudo tee scheduler
echo deadline |sudo tee scheduler
Outliers
A data point on a graph or in a set of results that is very much bigger or smaller than the next nearest data point.
WD Velociraptor 10000 RPM (SATA)
Seagate Cheetah 15000 RPM (SAS)
FusionIO ioDrive II (PCI-Express)
RAID0 across 15K SAS, 10K SATA, 7.2K SAS, SSD SATA
RAID0 across 15K SAS, 10K SATA, 7.2K SAS, SSD SATA
RAID0 across 15K SAS, 10K SATA, 7.2K SAS, SSD SATA
iostat -x 5
avg-cpu: %user %nice %system %iowait %steal %idle
2.72 0.00 1.31 19.93 0.00 76.04
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util
sdb 0.00 0.00 185.60 0.00 95027.20 0.00 1024.00 3.17 17.08 17.08 0.00 2.78 51.54
sdc 0.00 0.00 185.20 0.00 94822.40 0.00 1024.00 82.46 435.46 435.46 0.00 5.40 100.00
sda 0.00 0.00 184.40 0.00 94412.80 0.00 1024.00 0.89 4.83 4.83 0.00 1.02 18.80
sdd 0.00 0.00 186.40 0.00 95436.80 0.00 1024.00 7.46 40.17 40.17 0.00 4.91 91.52
md0 0.00 0.00 742.40 0.00 380108.80 0.00 1024.00 0.00 0.00 0.00 0.00 0.00 0.00
avg-cpu: %user %nice %system %iowait %steal %idle
1.58 0.00 1.03 23.29 0.00 74.10
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util
sdb 0.00 0.00 184.00 0.00 94208.00 0.00 1024.00 1.90 10.36 10.36 0.00 2.41 44.40
sdc 0.00 0.00 185.40 0.00 94924.80 0.00 1024.00 89.72 461.72 461.72 0.00 5.39 100.00
sda 0.00 0.00 184.00 0.00 94208.00 0.00 1024.00 0.87 4.77 4.77 0.00 1.03 19.00
sdd 0.00 0.00 184.40 0.00 94209.60 0.00 1021.80 3.78 20.50 20.50 0.00 4.16 76.74
md0 0.00 0.00 730.00 0.00 373556.80 0.00 1023.44 0.00 0.00 0.00 0.00 0.00 0.00
avg-cpu: %user %nice %system %iowait %steal %idle
2.77 0.00 1.71 9.70 0.00 85.81
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util
sdb 0.00 0.00 187.60 0.00 96051.20 0.00 1024.00 2.31 12.24 12.24 0.00 2.58 48.32
sdc 0.00 0.00 186.60 0.00 95539.20 0.00 1024.00 79.91 457.97 457.97 0.00 5.36 100.00
sda 0.00 0.00 188.80 0.00 96665.60 0.00 1024.00 0.90 4.74 4.74 0.00 1.02 19.28
sdd 0.00 0.00 187.80 0.00 95848.80 0.00 1020.75 5.81 30.84 30.84 0.00 4.73 88.74
md0 0.00 0.00 755.80 0.00 386664.80 0.00 1023.19 0.00 0.00 0.00 0.00 0.00 0.00
How It's Made
Where the magic happens
fio
[global]
rw=randread
blocksize=4096
ioengine=sync
norandommap=1
direct=1
iodepth=1
iodepth_batch=1
iodepth_batch_complete=1
group_reporting=1
ramp_time=5
time_based=1
runtime=600s
randrepeat=0
unlink=0
numjobs=1
nrfiles=4
size=100g
181GB of raw data
11G effio/suites/i-c39a1acda-full
22G effio/suites/ip-172-31-12-247-full-2014-09-07
51G effio/suites/zorak-full-2014-09-04
34G effio/suites/moltar-full-2014-09-08
39G effio/suites/zorak-full-fio-2014-09-09
14G effio/suites/zorak-full-raijin-2014-09-10
10G effio/suites/zorak-raid0-hdd-hdd-hdd-ssd
181G
