In a Debian stretch, I did some quick tests for a 500GB Samsung SSD 840 read speed at all the different partitions and I cannot understand the results. My understanding so far was that the disk could not know anything about the partitioning scheme, so it should have a somewhat consistent performance throughout the storage area. The disk has already data written in all partitions during the last 3-4 years or something.
root@debian9:~# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 465.8G 0 disk
├─sda1 8:1 0 19.4G 0 part
├─sda2 8:2 0 100M 0 part
├─sda3 8:3 0 136.9G 0 part
├─sda5 8:5 0 68.4G 0 part
├─sda6 8:6 0 97.7G 0 part
├─sda7 8:7 0 45.7G 0 part /
└─sda8 8:8 0 97.7G 0 part
I also deleted data and did a blkdiscard in a partition (/dev/sda8) and the speed was raised from 100 to 500MB/sec for both read and write at this partition. I did not notice any performance improvements at the other partitions.
The tests were performed with hdparm and the disk did not have any other I/O transfers at the same time.
root@debian9:~# for i in /dev/sda*
> do
> hdparm -t $i
> done
/dev/sda:
Timing buffered disk reads: 1482 MB in 3.00 seconds = 493.47 MB/sec
/dev/sda1:
Timing buffered disk reads: 1478 MB in 3.00 seconds = 492.19 MB/sec
/dev/sda2:
Timing buffered disk reads: 100 MB in 0.61 seconds = 164.61 MB/sec
/dev/sda3:
Timing buffered disk reads: 410 MB in 3.01 seconds = 136.29 MB/sec
/dev/sda4: No such device or address
/dev/sda5:
Timing buffered disk reads: 272 MB in 3.06 seconds = 88.99 MB/sec
/dev/sda6:
Timing buffered disk reads: 336 MB in 3.00 seconds = 111.83 MB/sec
/dev/sda7:
Timing buffered disk reads: 1456 MB in 3.00 seconds = 484.78 MB/sec
/dev/sda8:
Timing buffered disk reads: 1514 MB in 3.00 seconds = 504.55 MB/sec
My guess for this speed variations is that the disk has independent areas which do not affect each other or something?
On the other hand, why did blkdiscard influenced also the read speed so much?
