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URL:
https://askubuntu.com/q/939990
Title:
Samsung SSD 850 Pro slow speed
ID:
/2017/07/26/Samsung-SSD-850-Pro-slow-speed
Created:
July 26, 2017
Edited: July 26, 2017
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April 8, 2024
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SATA II channel (3 Gbps) vs. SATA III channel (6 Gbps)
Looking at your timings it is similar to my /dev/sdc
$ sudo hdparm -tT /dev/sdc
/dev/sdc:
Timing cached reads: 20494 MB in 2.00 seconds = 10255.92 MB/sec
Timing buffered disk reads: 812 MB in 3.00 seconds = 270.63 MB/sec
What you are hoping for is timings like my /dev/sda
$ sudo hdparm -tT /dev/sda
/dev/sda:
Timing cached reads: 21598 MB in 2.00 seconds = 10809.23 MB/sec
Timing buffered disk reads: 1566 MB in 3.00 seconds = 521.44 MB/sec
The explanation can be found using dmesg | grep SATA
$ dmesg | grep SATA
[ 1.177247] ahci 0000:00:1f.2: AHCI 0001.0300 32 slots 6 ports 6 Gbps 0xf impl SATA mode
[ 1.202732] ata1: SATA max UDMA/133 abar m2048@0xf1618000 port 0xf1618100 irq 27
[ 1.202735] ata2: SATA max UDMA/133 abar m2048@0xf1618000 port 0xf1618180 irq 27
[ 1.202736] ata3: SATA max UDMA/133 abar m2048@0xf1618000 port 0xf1618200 irq 27
[ 1.202739] ata4: SATA max UDMA/133 abar m2048@0xf1618000 port 0xf1618280 irq 27
[ 1.521294] ata1: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
[ 1.521318] ata3: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
[ 1.521337] ata2: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
[ 1.521356] ata4: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
Both /dev/sda and /dev/sdc are SATA III SSD’s but sda is on a 6 Gbps bus (ata1) and sdc is on a 3 Gbps bus.
Comparison to SATA II 500GB HDD on a SATA III Channel
For comparison sakes here are the results of a 5400 rpm SATA II 500 GB HDD running on a SATA III (6 Gbps) channel:
$ sudo hdparm -tT /dev/sdb
/dev/sdb:
Timing cached reads: 20632 MB in 2.00 seconds = 10325.32 MB/sec
Timing buffered disk reads: 340 MB in 3.02 seconds = 112.76 MB/sec
Summary
This is a laptop and only has two SATA channels:
- ata1 and ata2 are SATA III channels (6 Gbps)
- ata3 and ata4 are SATA II channels (3 Gbps)
Linux/Ubuntu matches the device’s SATA ability and channel’s SATA ability to the lowest common denominator:
- ata1 has a 240GB SSD SATA III attached.
- ata2 has a 500GB HDD SATA II attached to SATA III channel.
- ata3 has a 120GB PCIe half-height SSD SATA III attached to SATA II channel.
- ata4 has a CD/DVD optical drive SATA I (1.5 Gbps) attached to SATA II channel.