Some disk settings I adjusted

Given the fact I now have an SSD drive running the /boot and root partition I do want to make the most of it. So in order to improve and keep this improvement over time I did the following:

I first reduce the amount of "swappiness" to the minimum. The box has 16G ram so I have enough headroom plus I move the swap partition to the spinning disk.

In sysctl -a:

vm.swappiness = 1
vm.vfs_cache_pressure = 100

I enabled the discard option on the ext4 filesystems to enable TRIM in order to free up block upon release

In fstab:
/dev/mapper/vg_monster-lv_root /                       ext4    defaults,discard        1 1
UUID=3de72813-da36-4a6e-89e1-4805b0fc03ea /boot                   ext4    defaults        1 2
/dev/sdb1             swap                    swap    defaults        0 0

So the vg_monster-lv_root sits on the SSD drive and the swap space + /home partition on the spinning rust.

There are two reasons for this.
1. I can monitor the rotating disk for increasing faults. By default any spinning disk has some spare blocks so it can either try and rewrite the failing block to a good one or just mark the block as bad so I would most likely lose just one block or sector.
2. SSD's don't have the option for marking a single block as bad. Most likely an entire cell fails which in general will brick the disk. I can rebuild an OS fairly quickly but my homedrive with all settings and data is a much larger piece of work. In addition it's much easier to rsync a single directory that the entire box to another medium. 🙂

In addition I changed the default CFQ scheduler to deadline in other to get the optimum number of queues and timeout deadlocks on read/write operations. This scheduler prevents from processes having to wait for requests by other processes too long causing them to timeout.

[[email protected] ~]# cat /sys/block/sda/queue/scheduler
noop [deadline] cfq
[[email protected] ~]# cat /sys/block/sdb/queue/scheduler
noop deadline [cfq]
[[email protected] ~]#

I added some udev rules to sort this out on boot:

[[email protected] ~]# cat /etc/udev/rules.d/60-disk-scheduler.rules
# set deadline scheduler for non-rotating disks
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="deadline"

# set cfq scheduler for rotating disks
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="1", ATTR{queue/scheduler}="cfq"

Some more to come when I figure some stuff out.


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About Erwin van Londen

Master Technical Analyst at Hitachi Data Systems
Linux , ,