[mythtv-users] 8 Port SATA PCIx card
agraham at g-b.net
Mon Jul 20 01:25:55 UTC 2009
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
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 - - - - -
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