roles/common: Set I/O scheduler via udev

All servers with non-rotating disks (SSDs) should be running noop,
and the rest should be running deadline.

Signed-off-by: Alan Orth <alan.orth@gmail.com>

roles/common/tasks/main.yml

@@ -43,6 +43,10 @@
   when: ansible_distribution == 'Ubuntu'
   template: src=rc.local_{{ ansible_distribution }}.j2 dest=/etc/rc.local owner=root group=root mode=0755
 
+- name: Set I/O scheduler
+  template: src=etc/udev/rules.d/60-scheduler.rules.j2 dest=/etc/udev/rules.d/60-scheduler.rules owner=root group=root mode=0644
+  tags: udev
+
 - include: ssh-keys.yml
   tags: ssh-keys
 

roles/common/templates/etc/udev/rules.d/60-scheduler.rules.j2

@@ -0,0 +1,20 @@
+# set noop scheduler for non-rotating disks (SSD)
+# the glob matches sd* on physical hosts, xvd* on Xen hosts, and vd* on KVM hosts
+ACTION=="add|change", KERNEL=="xvd[a-z]|[sv]d[a-z]", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="noop"
+
+# set deadline scheduler for rotating disks
+# the glob matches sd* on physical hosts, xvd* on Xen hosts, and vd* on KVM hosts
+# 
+# newer KVM guests (Ubuntu 14.04 at least, so Linux >=3.13) using virtio vda don't
+# allow it to be set, but it's non fatal so let's just set it for now
+ACTION=="add|change", KERNEL=="xvd[a-z]|[sv]d[a-z]", ATTR{queue/rotational}=="1", ATTR{queue/scheduler}="deadline"
+
+{% if 'storage' in group_names %}
+## set disk tweaks
+## see: http://www.fhgfs.com/wiki/wikka.php?wakka=StorageServerTuning
+## see: http://community.gluster.org/a/linux-kernel-tuning-for-glusterfs/
+# give the IO scheduler more flexibility by increasing the number of schedulable requests (queue_depth * 2):
+ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/nr_requests}="512"
+# To improve throughput for sequential reads, increase the maximum amount of read-ahead data. The actual amount of read-ahead is adaptive, so using a high value here won't harm performance for small random access.
+ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/read_ahead_kb}="4096"
+{% endif %}