During a recent install of FreeBSD 9.1 onto a gmirror, it was pointed out that my disk partitions were not aligned. Today, I’ll look at how that affects performance, both before and after alignment.
Last night, I installed FreeBSD 9.1 onto a separate HDD, which I’ll use as a floater. I can attach this HDD to any system I need to work on without booting from the main HDD. In attached this HDD to the new server so I could look at the installed HDD. Here is what I found:
$ gpart show ada1 ada2
=> 63 488397105 ada1 MBR (232G)
63 4095 - free - (2M)
4158 488392947 1 freebsd [active] (232G)
488397105 63 - free - (31k)
=> 63 488397105 ada2 MBR (232G)
63 4095 - free - (2M)
4158 488392947 1 freebsd [active] (232G)
488397105 63 - free - (31k)
As you can see here, the FreeBSD partition starts at 4158, which is probably not on a physical sector, unless the HDD has some odd numbering system I am not familiar with.
Just what are these HDD?
ada1 at ahcich1 bus 0 scbus1 target 0 lun 0 ada1: <ST250DM000-1BD141 KC45> ATA-8 SATA 3.x device ada1: 300.000MB/s transfers (SATA 2.x, UDMA6, PIO 8192bytes) ada1: Command Queueing enabled ada1: 238475MB (488397168 512 byte sectors: 16H 63S/T 16383C) ada1: Previously was known as ad6 ada2 at ahcich2 bus 0 scbus2 target 0 lun 0 ada2: <WDC WD2500AAKX-08ERMA0 19.01H19> ATA-8 SATA 3.x device ada2: 300.000MB/s transfers (SATA 2.x, UDMA5, PIO 8192bytes) ada2: Command Queueing enabled ada2: 238475MB (488397168 512 byte sectors: 16H 63S/T 16383C) ada2: Previously was known as ad8
NOTE: both drives mention 3.x devicebut then say SATA 2.x on the next line. What’s up with that?
Perhaps it is because the motherboard does only SATA 2.
ada1 is a ST250DM000-1BD141, otherwise known as a Seagate Barracuda ST250DM000 250GB 7200 RPM 16MB Cache SATA 6.0Gb/s 3.5″. The data sheet says it has 512 byte sectors.
ada2 is a WDC WD2500AAKX-08ERMA0, which is a Western Digital WD Blue WD2500AAKX 250GB 7200 RPM 16MB Cache SATA 6.0Gb/s. The spec sheet does not state a sector size. Hmmm.
OK. Let’s start the tests. This one took 4.5 hours
$ sudo ./phybs -rw -l 1024 /dev/ada1 count size offset step msec tps kBps 131072 1024 0 4096 2032548 64 64 131072 1024 512 4096 2096942 62 62 65536 2048 0 8192 898654 72 145 65536 2048 512 8192 795774 82 164 65536 2048 1024 8192 852636 76 153 32768 4096 0 16384 99953 327 1311 32768 4096 512 16384 369648 88 354 32768 4096 1024 16384 472211 69 277 32768 4096 2048 16384 475392 68 275 16384 8192 0 32768 89769 182 1460 16384 8192 512 32768 197861 82 662 16384 8192 1024 32768 289654 56 452 16384 8192 2048 32768 275401 59 475 16384 8192 4096 32768 64115 255 2044 $
Let’s try ada2:
$ sudo ./phybs -rw -l 1024 /dev/ada2 count size offset step msec tps kBps 131072 1024 0 4096 205871 636 636 131072 1024 512 4096 219599 596 596 65536 2048 0 8192 174184 376 752 65536 2048 512 8192 161844 404 809 65536 2048 1024 8192 176060 372 744 32768 4096 0 16384 144485 226 907 32768 4096 512 16384 157527 208 832 32768 4096 1024 16384 158052 207 829 32768 4096 2048 16384 143603 228 912 16384 8192 0 32768 126661 129 1034 16384 8192 512 32768 133836 122 979 16384 8192 1024 32768 125020 131 1048 16384 8192 2048 32768 118295 138 1108 16384 8192 4096 32768 114937 142 1140
Now, if only I knew what those meant….
See this post for an explanation of phybs’s output.
Quick primer: look at the second, third and last columns on each line. The second is the block size, the third is the offset and the last is the throughput. With the Seagate, you can clearly see that it performs best when both the block size and offset are multiples of 4096. The WD drive, on the other hand, doesn’t seem to prefer any particular block size or alignment, which indicates that unlike the Seagate, it is not a 4k drive.
(you got the wrong product sheet for the Seagate; the right one clearly says 4096 bytes)
However, both are dog slow—nowhere near what I’d expect from modern SATA drives. With 8192-byte writes, you should be getting around 20 to 30 MBps, and you’re only getting around 1 or 2 MBps. Can you try a sequential test?
I wonder why both drives are so slow. I will try a sequential write. Are you expecting something like a ‘dd if=/dev/zero’?
[dan@floater:~] $ sudo dd if=/dev/zero of=/dev/ada1 count=100000
100000+0 records in
100000+0 records out
51200000 bytes transferred in 7.033895 secs (7279040 bytes/sec)
[dan@floater:~] $ sudo dd if=/dev/zero of=/dev/ada1 count=600000
600000+0 records in
600000+0 records out
307200000 bytes transferred in 42.317677 secs (7259378 bytes/sec)
$ sudo dd if=/dev/zero of=/dev/ada1 count=1600000
1600000+0 records in
1600000+0 records out
819200000 bytes transferred in 112.384917 secs (7289234 bytes/sec)
Still, that’s only 6.9 MB / s
Terrible. Why so terrible?
Let’s try the other drive:
$ sudo dd if=/dev/zero of=/dev/ada1 count=1600000
1600000+0 records in
1600000+0 records out
819200000 bytes transferred in 112.384917 secs (7289234 bytes/sec)
$ sudo dd if=/dev/zero of=/dev/ada2 count=1600000000
1600000+0 records in
1600000+0 records out
819200000 bytes transferred in 135.923697 secs (6026911 bytes/sec)
About that data sheet, it is interesting that when I go to your link, then click on support, I get taken to my link.
But now I see the ‘Barracuda Data Sheet (455 KB)‘ link at the top of the page.
I have updated my post with the real link. Thank you.
Success. Try a bigger block size:
$ sudo dd if=/dev/zero of=/dev/ada1 count=1600000 bs=32k
Password:
There’s a lot of it about, you know.
Password:
1600000+0 records in
1600000+0 records out
52428800000 bytes transferred in 365.299993 secs (143522587 bytes/sec)
The other HDD is:
$ sudo dd if=/dev/zero of=/dev/ada2 count=1600000 bs=32k
1600000+0 records in
1600000+0 records out
52428800000 bytes transferred in 435.509907 secs (120384862 bytes/sec)
That’s 114.807951 MB / s
And the first one is 136.873805 MB / s
I think everything is in order.
I may buy a SATA 3 card.