[ovirt-users] Re: Tuning Gluster Writes

Sun, 14 Apr 2019 10:04:59 -0700 

On 2019-04-14 12:07, Alex McWhirter wrote:

On 2019-04-13 03:15, Strahil wrote:

Hi,

What is your dirty  cache settings on the gluster servers  ?

Best Regards,
Strahil NikolovOn Apr 13, 2019 00:44, Alex McWhirter <a...@triadic.us> wrote: 

I have 8 machines acting as gluster servers. They each have 12 drives
raid 50'd together (3 sets of 4 drives raid 5'd then 0'd together as
one).

They connect to the compute hosts and to each other over lacp'd 10GB
connections split across two cisco nexus switched with VPC.

Gluster has the following set.

performance.write-behind-window-size: 4MB
performance.flush-behind: on
performance.stat-prefetch: on
server.event-threads: 4
client.event-threads: 8
performance.io-thread-count: 32
network.ping-timeout: 30
cluster.granular-entry-heal: enable
performance.strict-o-direct: on
storage.owner-gid: 36
storage.owner-uid: 36
features.shard: on
cluster.shd-wait-qlength: 10000
cluster.shd-max-threads: 8
cluster.locking-scheme: granular
cluster.data-self-heal-algorithm: full
cluster.server-quorum-type: server
cluster.quorum-type: auto
cluster.eager-lock: enable
network.remote-dio: off
performance.low-prio-threads: 32
performance.io-cache: off
performance.read-ahead: off
performance.quick-read: off
auth.allow: *
user.cifs: off
transport.address-family: inet
nfs.disable: off
performance.client-io-threads: on
I have the following sysctl values on gluster client and servers, using 
libgfapi, MTU 9K

net.core.rmem_max = 134217728
net.core.wmem_max = 134217728
net.ipv4.tcp_rmem = 4096 87380 134217728
net.ipv4.tcp_wmem = 4096 65536 134217728
net.core.netdev_max_backlog = 300000
net.ipv4.tcp_moderate_rcvbuf =1
net.ipv4.tcp_no_metrics_save = 1
net.ipv4.tcp_congestion_control=htcp
reads with this setup are perfect, benchmarked in VM to be about 770MB/s sequential with disk access times of < 1ms. Writes on the other hand are all over the place. They peak around 320MB/s sequential write, which is 
what i expect but it seems as if there is some blocking going on.

During the write test i will hit 320MB/s briefly, then 0MB/s as disk
access time shoot to over 3000ms, then back to 320MB/s. It averages out 
to about 110MB/s afterwards.

Gluster version is 3.12.15 ovirt is 4.2.7.5
Any ideas on what i could tune to eliminate or minimize that blocking? 
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Just the vdsm defaults

vm.dirty_ratio = 5
vm.dirty_background_ratio = 2

these boxes only have 8gb of ram as well, so those percentages should
be super small.
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doing a gluster profile my bricks give me some odd numbers.
%-latency Avg-latency Min-Latency Max-Latency No. of calls Fop --------- ----------- ----------- ----------- ------------ ---- 0.00 131.00 us 131.00 us 131.00 us 1 FSTAT 0.01 104.50 us 77.00 us 118.00 us 14 STATFS 0.01 95.38 us 45.00 us 130.00 us 16 STAT 0.10 252.39 us 124.00 us 329.00 us 61 LOOKUP 0.22 55.68 us 16.00 us 180.00 us 635 FINODELK 0.43 543.41 us 50.00 us 1760.00 us 125 FSYNC 1.52 573.75 us 76.00 us 5463.00 us 422 FXATTROP 97.72 7443.50 us 184.00 us 34917.00 us 2092 WRITE
%-latency Avg-latency Min-Latency Max-Latency No. of calls Fop --------- ----------- ----------- ----------- ------------ ---- 0.00 0.00 us 0.00 us 0.00 us 70 FORGET 0.00 0.00 us 0.00 us 0.00 us 1792 RELEASE 0.00 0.00 us 0.00 us 0.00 us 23422 RELEASEDIR 0.01 126.20 us 80.00 us 210.00 us 20 FSTAT 0.06 102.81 us 26.00 us 162.00 us 230 STATFS 0.06 93.51 us 18.00 us 174.00 us 261 STAT 0.57 239.13 us 103.00 us 391.00 us 997 LOOKUP 0.59 59.07 us 15.00 us 6554.00 us 4208 FINODELK 1.31 506.71 us 50.00 us 2735.00 us 1077 FSYNC 2.53 389.07 us 65.00 us 5510.00 us 2720 FXATTROP 28.24 498.18 us 134.00 us 3513.00 us 23688 READ 66.64 4971.59 us 184.00 us 34917.00 us 5601 WRITE
%-latency Avg-latency Min-Latency Max-Latency No. of calls Fop --------- ----------- ----------- ----------- ------------ ---- 0.00 92.33 us 83.00 us 97.00 us 3 FSTAT 0.01 87.81 us 35.00 us 123.00 us 16 STAT 0.01 101.64 us 67.00 us 133.00 us 14 STATFS 0.11 235.67 us 149.00 us 320.00 us 51 LOOKUP 0.17 497.46 us 170.00 us 771.00 us 35 FSYNC 0.43 247.58 us 81.00 us 983.00 us 181 FXATTROP 0.43 49.37 us 14.00 us 177.00 us 914 FINODELK 98.83 5591.06 us 192.00 us 29586.00 us 1850 WRITE
%-latency Avg-latency Min-Latency Max-Latency No. of calls Fop --------- ----------- ----------- ----------- ------------ ---- 0.00 92.33 us 83.00 us 97.00 us 3 FSTAT 0.01 87.81 us 35.00 us 123.00 us 16 STAT 0.01 101.64 us 67.00 us 133.00 us 14 STATFS 0.11 235.67 us 149.00 us 320.00 us 51 LOOKUP 0.17 497.46 us 170.00 us 771.00 us 35 FSYNC 0.43 247.58 us 81.00 us 983.00 us 181 FXATTROP 0.43 49.37 us 14.00 us 177.00 us 914 FINODELK 98.83 5591.06 us 192.00 us 29586.00 us 1850 WRITE
%-latency Avg-latency Min-Latency Max-Latency No. of calls Fop --------- ----------- ----------- ----------- ------------ ---- 0.00 102.40 us 69.00 us 130.00 us 5 FSTAT 0.00 94.50 us 32.00 us 130.00 us 14 STATFS 0.03 231.25 us 97.00 us 332.00 us 55 LOOKUP 0.05 985.54 us 402.00 us 1371.00 us 24 READ 0.09 397.99 us 89.00 us 1072.00 us 113 FSYNC 0.23 384.93 us 68.00 us 3276.00 us 286 FXATTROP 11.66 4835.83 us 214.00 us 25386.00 us 1158 WRITE 87.93 87398.97 us 16.00 us 1325513.00 us 483 FINODELK
%-latency Avg-latency Min-Latency Max-Latency No. of calls Fop --------- ----------- ----------- ----------- ------------ ---- 0.00 0.00 us 0.00 us 0.00 us 83 FORGET 0.00 0.00 us 0.00 us 0.00 us 2103 RELEASE 0.00 0.00 us 0.00 us 0.00 us 23419 RELEASEDIR 0.01 114.54 us 51.00 us 175.00 us 80 FSTAT 0.02 94.78 us 28.00 us 176.00 us 230 STATFS 0.18 364.51 us 51.00 us 1072.00 us 531 FSYNC 0.19 221.18 us 97.00 us 432.00 us 936 LOOKUP 0.34 273.10 us 68.00 us 3276.00 us 1354 FXATTROP 12.70 3875.57 us 179.00 us 29246.00 us 3534 WRITE 12.76 560.97 us 141.00 us 4705.00 us 24547 READ 73.80 44651.79 us 12.00 us 1984451.00 us 1783 FINODELK
%-latency Avg-latency Min-Latency Max-Latency No. of calls Fop --------- ----------- ----------- ----------- ------------ ---- 0.00 130.50 us 127.00 us 134.00 us 2 FSTAT 0.02 87.12 us 36.00 us 113.00 us 16 STAT 0.02 107.86 us 76.00 us 117.00 us 14 STATFS 0.05 136.09 us 26.00 us 630.00 us 32 READ 0.14 235.45 us 115.00 us 315.00 us 55 LOOKUP 0.35 65.89 us 18.00 us 1283.00 us 477 FINODELK 0.81 648.49 us 105.00 us 3673.00 us 113 FSYNC 1.98 624.26 us 74.00 us 5532.00 us 286 FXATTROP 96.63 7515.45 us 263.00 us 37343.00 us 1158 WRITE
%-latency Avg-latency Min-Latency Max-Latency No. of calls Fop --------- ----------- ----------- ----------- ------------ ---- 0.00 0.00 us 0.00 us 0.00 us 83 FORGET 0.00 0.00 us 0.00 us 0.00 us 2103 RELEASE 0.00 0.00 us 0.00 us 0.00 us 23422 RELEASEDIR 0.01 123.21 us 49.00 us 194.00 us 29 FSTAT 0.09 101.08 us 33.00 us 149.00 us 230 STATFS 0.10 94.62 us 30.00 us 325.00 us 261 STAT 0.49 71.46 us 15.00 us 1283.00 us 1779 FINODELK 0.86 239.23 us 72.00 us 397.00 us 936 LOOKUP 0.92 447.62 us 41.00 us 3673.00 us 531 FSYNC 1.80 344.20 us 71.00 us 5532.00 us 1354 FXATTROP 28.40 519.98 us 23.00 us 8811.00 us 14159 READ 67.33 4939.29 us 177.00 us 37343.00 us 3534 WRITE
Looks like two of the bricks are seeing excessive latency over the rest which seem more or less the same +/- 1-3ms.
Looks like i need to debug those two bricks? Obviously +/- 50ms is unacceptable, but is +/- 3ms also unreasonable for HDD's? 
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