SAS drives seem slow

[Josh Paetzel]

On Feb 26, 2009, at 12:28 AM, Wojciech Puchar wrote:

>> FreeBSD services.tcbug.org 8.0-CURRENT FreeBSD 8.0-CURRENT #0: Mon  
>> Feb 16 21:07:14 UTC 2009     root@:/usr/obj/usr/src/sys/SERVICES   
>> amd64
>>
>> But 6.x and 7.x give similar results.
>>
>> The disks themselves are capable of sequential read/write in the  
>> 180 Meg/sec range, so I'm trying to understand why I'm being told  
>> they are 100 Meg/sec, and why that seems to be their real world  
>> performance cap.
>>
>
> probably you use RAID5


Hrmm, I should have included drive configuration.

root at services /home/jpaetzel ->tw_cli /c0 show

Unit  UnitType  Status         %RCmpl  %V/I/M  Stripe  Size(GB)   
Cache  AVrfy
------------------------------------------------------------------------------
u0    RAID-1    OK             -       -       -       135.031    
ON     ON
u1    RAID-1    OK             -       -       -       298.013    
ON     ON

VPort Status         Unit Size      Type  Phy Encl-Slot    Model
------------------------------------------------------------------------------
p0    OK             u0   136.98 GB SAS   0   -            FUJITSU  
MBA3147RC
p1    OK             u0   136.98 GB SAS   1   -            FUJITSU  
MBA3147RC
p2    OK             u1   298.09 GB SATA 2   -            WDC  
WD3200AAKS-00SB
p3    OK             u1   298.09 GB SATA 3   -            WDC  
WD3200AAKS-00SB


But I get similar results when I connect just a single SAS drive and  
export it as a raw device.  It's also worth noting that the SATA drive  
array is reported as 100MB/sec transfers, even though the drives  
aren't capable of anything close to that, unless they are reading from  
cache, in which case SATA2 is capable of more like 300MB/sec...but  
then so is SAS...


Thanks,

Josh Paetzel