I was looking at things on the new server that I had just setup today and I noticed that the SSD was being written to at a continuous 35MB/s. This was as a result of the zoneminder /var/tmp/zm being located on the primary disk.
The solution was to add a line to /etc/fstab and dedicated an 8GB RAM disk to resolve my issue. The running occupied size for my setup before was roughly 5GB. Here is the /etc/fstab line:
tmpfs /var/tmp/zm tmpfs rw,nodev,nosuid,size=8G 0 0
Whilst researching this solution I stumbled across a bit of mdraid optimization I hadn’t done or tested for yet. That was checking the stripe cache size for
The default was 256. I tried several different sizes, each time running hdparm -Tt /dev/md127 for a quick and dirty test to figure out which seems to work best. 32768 yielded the best results.
With the 16 disks in a RAID6 using two LSI Logic / Symbios Logic 9207-8i SAS2.1 HBA 8 port adapters I was able to achieve 2GB/s read and nearly 950MB/s sustained write.
time cp /ramdisk/10g.bin /raid/
time cp /raid/10g.bin /ramdisk/
hdparm -Tt /dev/md127
Timing cached reads: 10886 MB in 2.00 seconds = 5445.73 MB/sec
Timing buffered disk reads: 5864 MB in 3.00 seconds = 1954.45 MB/sec
This isn’t the best in the world really, but it is not bad either! This kind of capacity coupled with a large amount of disks allows me to record a lot of CCTV footage. Though, I suppose I haven’t explained how all of this works.
Stock blockdev readahead on my system was 28672.