Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

I've experimented with different striped volumes in vinum under FreeBSD 8.2-release. I have current hardware (Intel i5 processor, adequate MB and 8GB RAM).

My test-setup consists of 2 or 4 disks in a volume, each disk is 2TB, "Green" line Seagate and Western Digital; i.e. consumer disks at 5400RPM. These are in my server, while my desktop that's connected to it (via Gbit LAN) has a quick SSD.

My problem is that I get better performance (i.e. read/write speeds) over my Gbit LAN when I access my single "Black" Western Digital 2TB, than when I access my vinum volumes.

  • Black WD single disk: read = write = 90-105 MB/s
  • vinum volumes, all setups: read = 80 MB/s ; write = 50 MB/s

The vinum configurations I've tried are:

test1:

drive a device /dev/ad32
drive b device /dev/ad34
drive c device /dev/ad26
drive d device /dev/ad28
volume test1
  plex org striped 512k
    sd length 2048m drive a
    sd length 2048m drive b
    sd length 2048m drive c
    sd length 2048m drive d

test2:

drive a device /dev/ad32
drive b device /dev/ad34
volume test2
  plex org striped 512k
    sd length 1907728m drive a
    sd length 1907728m drive b

I've tested test1 with different stripe lengths (512k, 64k, 2048k), but the speeds are the same. Also, I notice no difference in speeds between test1 and test2, which I find very strange, considering these are striped volumes and disk-count therefore should matter.

Does anyone have a clue why this happens and what I can do to tune/speed-up vinum to at least outspeed my single HDD? Should I consider other options for performance (ZFS w/RAIDZ etc)?

More info (edit)

dmesg about the disks:

  • ad26: 1907729MB [ST2000DL003 9VT166 CC32] at ata13-master UDMA100 SATA 6Gb/s
  • ad28: 1907729MB [ST2000DL003 9VT166 CC32] at ata14-master UDMA100 SATA 3Gb/s
  • ad32: 1907729MB [WDC WD20EARX-00PASB0 51.0AB51] at ata16-master UDMA100 SATA 3Gb/s
  • ad34: 1907729MB [WDC WD20EARX-00PASB0 51.0AB51] at ata17-master UDMA100 SATA 3Gb/s

All disks are connected to onboard SATA-controller on my motherboard; Asus P8P67 Deluxe.

When testing ad32 as a single disk, I get write-speed at about 60-70MB/s, read-speed at about 80-90MB/s.

All testing done with one large file of about 2.5GB.

The point: my disks perform slower in a striped volume than alone... Suggestions?

share|improve this question
1  
Your problem could be those "green" model disks. What performance do you get out of them? –  MikeyB Oct 7 '11 at 1:25
    
@MikeyB In fact, I haven't tested them as single disks yet, but if the fact is that they're slow, couldn't I at least expect faster speeds with an array of 4 green disks than an array of 2 green disks; both arrays striped? –  poplitea Oct 7 '11 at 1:29
2  
Let's get all the information out - individual disk speed, which disk is which, type of controller (SAS? SATA? Onboard? Expansion card?) –  MikeyB Oct 7 '11 at 1:33
    
@MikeyB I suppose that's better :-) Now I've edited my post with more info. –  poplitea Oct 7 '11 at 1:46
add comment

1 Answer 1

up vote 3 down vote accepted

Based on what you've posted so far my guess is that your striped volume is almost certainly being hampered by slower drives (I see one 6Gb/sec link and 3 3Gb/sec links - I'm willing to bet the 3Gb/sec drives also have lower general operating specs.


Like @MikeyB said run speed tests for each disk individually - this will confirm my theory (or send you looking in another direction).
You can expect to see performance bounded by some function of the slowest disk in the array, with a hard upper limit at-or-around the SATA controller's maximum throughput.

You can also try running gstat when testing the array and see what kind of activity you've got on each disk - If the slower ones are maxing out that could be your culprit, and if the controller is pinned that's definitely an issue.

share|improve this answer
    
Thanks a lot! gstat is a useful tool I didn't know about. I found that ad26+ad28 performs fast in a 2-disk striped volume. About 120MB/s write and 80-90 MB/s read (strange with write>read?). In that setup ad26 is 20% busy, ad28 30%; according to gstat. I suppose this is because of the controller; 3 vs 6 Gb/s. I'll experiment further with single disks and test the controllers... –  poplitea Oct 7 '11 at 2:23
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.