[mythtv-users] 8 Port SATA PCIx card

[Albert Graham]

On 07/20/2009 01:39 AM, David Brodbeck wrote:
> Boleslaw Ciesielski wrote:
>> Gareth Glaccum wrote:
>>> The 3ware is really worth the extra price. You will have a GOOD 
>>> gui/webpage to administer the raid array, rather than needing to do 
>>> it from within the OS.
>>
>> Webpage? How does this card connect to the network without the OS? 
>> Does it have its own ethernet port?
>
> The 3ware cards use a daemon called 3dm2 to do this.  So technically 
> it's not "outside the OS," but it does mean you don't have to use the 
> command line if you don't want to.  Personally I prefer the tw_cli 
> command line utility.
>
> For real "outside the OS" RAID management you can use the 3ware BIOS 
> by hitting Alt-3 during boot, but that's rarely necessary except for 
> initial setup of a bootable array.
>
> Having used both, I can only see two clear advantages to a hardware 
> RAID card over software RAID, assuming CPU usage and bus bandwidth are 
> not limitations:
>
> - The 3ware hardware RAID cards fully support hot swapping failed 
> drives.  My personal experience is that this does not work with normal 
> SATA cards under Linux.
>
> - Booting from a hardware RAID is much easier to set up, and you don't 
> have to wonder if GRUB and the system BIOS will do the right thing if 
> the primary drive in a mirror fails.
>
> Neither of these are huge advantages for home use, since most home 
> users would just shut the system down to swap out a failed drive.


You in case you're interested, there is a very nice undocumented tw_cli 
command, that shows performance per drive in your array, it's handy when 
you have a single slow drive which could be impacting your entire array.

The command is:

# tw_cli /c0 set pmstat=on (which you should run with watch -n1)

The output is something like this


Setting Drive Performance Monitoring on /c6 to [on] ... Done.

Drive Performance Monitor Configuration for /c6 ...
Performance Monitor: ON
Version: 1
Max commands for averaging: 100
Max latency commands to save: 10
Requested data: Instantaneous Drive Statistics

                                Queue           Xfer         Resp
Port   Status           Unit   Depth   IOPs    Rate(MB/s)   Time(ms)
------------------------------------------------------------------------
p0     OK               u1     1       0       0.000        5
p1     OK               u1     1       0       0.000        4
p2     OK               u1     1       0       0.000        4
p3     OK               u1     1       0       0.000        4
p4     OK               u1     1       0       0.000        4
p5     OK               u1     1       0       0.000        5
p6     OK               u1     1       0       0.000        5
p7     OK               u1     1       0       0.000        4
p8     OK               u0     1       0       0.000        4
p9     OK               u0     1       0       0.000        4
p10    NOT-PRESENT      -      -       -       -            -
p11    NOT-PRESENT      -      -       -       -            -


Albert.