I'm testing the performances of my new SSD card, and it seems I'm stuck with sata2 speed even if my controller is sata3.

Here is the command I'm using.

dd if=tempfile of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1,1 GB) copied, 0,309558 s, 3,5 GB/s

I got 3,5GB/s even if my device is SATA3:

dmesg | grep SATA

[    7.035956] ahci 0000:00:1f.2: AHCI 0001.0300 32 slots 6 ports 6 Gbps 0x5 impl SATA mode
[    7.051861] ata1: SATA max UDMA/133 abar m2048@0xf7a16000 port 0xf7a16100 irq 43
[    7.051866] ata3: SATA max UDMA/133 abar m2048@0xf7a16000 port 0xf7a16200 irq 43
[    7.368593] ata1: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
[    7.368621] ata3: SATA link up 1.5 Gbps (SStatus 113 SControl 300)

hdparm -iI /dev/sda | grep SATA

Transport:          Serial, ATA8-AST, SATA 1.0a, SATA II Extensions, SATA Rev 2.5, SATA Rev 2.6, SATA Rev 3.0

Here is my controller:

lspci | grep SATA

00:1f.2 SATA controller: Intel Corporation 7 Series Chipset Family 6-port SATA Controller [AHCI mode] (rev 04)

This is the hdparam test:

 hdparm -I /dev/sda | grep -i speed
           *    Gen1 signaling speed (1.5Gb/s)
           *    Gen2 signaling speed (3.0Gb/s)
           *    Gen3 signaling speed (6.0Gb/s)

Partition alignment should be ok (I'm not 100% sure).

(parted) p                                                                
Model: ATA Samsung SSD 840 (scsi)
Disk /dev/sda: 250GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type     File system     Flags
 1      1049kB  92,9GB  92,9GB  primary  ext4
 4      92,9GB  94,0GB  1128MB  primary  ext4            boot
 2      94,0GB  241GB   147GB   primary  ext4
 3      241GB   250GB   9222MB  primary  linux-swap(v1)

(parted) align-check opt 1                                                
1 aligned
(parted) align-check opt 2
2 aligned
(parted) align-check opt 3
3 aligned
(parted) align-check opt 4
4 aligned

Bios is configured correctly with AHCI

My laptop is an Asus A55VD, SSD is Samsung EVO 840.

Why I'm having 3GB/s instead of 6GB/s?

Is perhaps my disk alignment not correct?


  • Your question confuses GB/s and Gb/s (Bytes and bits). SATA3 is rated at 6Gb/s, but this is only the interface speed, which the drive won't deliver. Most SSD drives are rated up to around 500MB/s (=4Gb/s). The 3.5GB/s (=28Gb/s) report from dd implies that you had previously accessed tempfile, so that most of its data were cached. The test using dd would have some validity only if the SSD had not been accessed since the system was booted, but it would then show less than the drive maximum because of OS and application overheads. – AFH Sep 6 '14 at 23:18

You must be missing something. SATA speed figures are measured in Gbit/s, what dd says, is in GByte/s. So, the numbers you got from dd are clearly not the speed you're looking for, as even SATA3 would not be able to do 3.5GByte/s (which is roughly 28Gbit/s) - the number you see must come from some OS internal buffer copy speed.

I don't know what you really want to test but dd is likely not the way to go. Measuring interface speed (between the SSD controller and your SATA controller) is usually not really useful, since there are normally other points in the path of the data, which are a lot narrower - for example the flash chips themselves. Tools like iobench, which can be configured to issue multiple parallel I/O requests, are usually a lot more useful.

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