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I have recently installed Ubuntu 17.04 on a brand new Samsung SSD 850 Pro. It seems to work fine. However the read and write speeds are roughly half of advertised

$ sudo hdparm -tT /dev/sda

/dev/sda:
 Timing cached reads:   9012 MB in  2.00 seconds = 4507.79 MB/sec
 Timing buffered disk reads: 808 MB in  3.01 seconds = 268.75 MB/sec

AHCI is enabled in BIOS and the system boots on UEFI.

The SSD has 6 partitions

$ sudo fdisk -l
Disk /dev/sda: 238.5 GiB, 256060514304 bytes, 500118192 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 8AAFFE6D-A829-46B5-B46F-ED4F7432F5B5

Device         Start       End   Sectors  Size Type
/dev/sda1       2048    485375    483328  236M EFI System
/dev/sda2     485376  39544831  39059456 18.6G Linux filesystem
/dev/sda3   39544832 117671935  78127104 37.3G Linux filesystem
/dev/sda4  117671936 133294079  15622144  7.5G Linux swap
/dev/sda5  133294080 259123199 125829120   60G Linux filesystem
/dev/sda6  259123200 468838399 209715200  100G Linux filesystem

Is there a problem in my setup? What might be the reason for lower than expected speeds? Any input is appreciated. Thanks in advance!

Update

Forgot to mention that the SSD is mounted on a 2010 Dell Latitude E6410 which I have just learned that has a SATA II connector. It seems then, the speeds I am getting are reasonable.

Thanks everyone for their comments and answers!

  • What is your motherboard model? What type of connector are you connecting it to? SATA 2 or SATA 3? – Terrance Jul 26 '17 at 13:41
  • I am not sure if this is the right command to answer your question but sudo dmesg | grep -i sata | grep 'link up' shows [ 1.813900] ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 300) [ 1.814236] ata2: SATA link up 1.5 Gbps (SStatus 113 SControl 300) – fatih Jul 26 '17 at 13:43
  • 3.0 Gbps is a SATA 2 connection. That will max at 300MB/s which is correct for your speeds. If you saw 6.0 Gbps that would be SATA 3 and it would max at 600 MB/s. I would check your motherboard to see if it has any SATA 3 connectors on it at all. – Terrance Jul 26 '17 at 13:50
  • You might be interested in this question where the author has the same SSD as you and invested many hours addressing speed issues: askubuntu.com/questions/881255/… – WinEunuuchs2Unix Jul 26 '17 at 14:26
3

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.

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