Re: mpt2sas logged messages

[Ric Wheeler <rwheeler@redhat.com>]

On 08/18/2009 12:09 PM, James Bottomley wrote:
> On Tue, 2009-08-18 at 11:53 -0400, Ric Wheeler wrote:
>> On 08/18/2009 10:57 AM, Greg KH wrote:
>>> On Tue, Aug 18, 2009 at 09:59:56AM -0400, Ric Wheeler wrote:
>>>
>>>> On 08/18/2009 09:25 AM, Greg KH wrote:
>>>>
>>>>> On Tue, Aug 18, 2009 at 09:18:30AM -0400, Ric Wheeler wrote:
>>>>>
>>>>>> We have a new toy to test very large&    slow storage with built up from 5
>>>>>> SAS expansion shelves (Promise Vtrak J-Class) with 60 S-ATA drives and
>>>>>> 16 SAS drives (the S-ATA drives each have a Promise Vtrak S-ATA MUX
>>>>>> adapter daughter card in the disk sled).
>>>>>>
>>>>>> The basic idea is to build a cheap&    slow test bed for file&    storage
>>>>>> system scalability. Collectively, we have about 120TB (raw) of capacity
>>>>>> to play with in one server.
>>>>>>
>>>>>> As we work through various issues, a couple of oddities popped out.
>>>>>>
>>>>>> The first is that udev grumbles during boot about "file name too long"
>>>>>> like the following:
>>>>>>
>>>>>> Aug 17 06:49:58 megadeth udevd-event[20447]: unable to create db file
>>>>>> '/dev/.udev/db/\x2fdevices\x2fpci0000:00\x2f0000:00:04.0\x2f0000:17:00.0\x2f0000:18:0a.0\x2f0000:1f:00.0\x2fhost11\x2fport-11:0\x2fexpander-11:0\x2fport-11:0:0\x2fexpander-11:1\x2fport-11:1:0\x2fexpander-11:2\x2fport-11:2:17\x2fexpander-11:3\x2fport-11:3:1\x2fend_device-11:3:1\x2fbsg\x2fend_device-11:3:1':
>>>>>> File name too long
>>>>>>
>>>>> Odd, what is the sysfs tree for this device?  You have expanders
>>>>> attached to ports attached to expanders?  How deep can you go?
>>>>>
>>>>> thanks,
>>>>>
>>>>> greg k-h
>>>>>
>>>> There are two dual-port SAS HBA's in the server that plug into the first of the
>>>> 5 SAS expansion shelves. Each shelf has two internal SAS loops and is daisy
>>>> chained to the next shelf....  This test is running with just the first 4
>>>> shelves active (although that fifth shelf is plugged in, just not used/active).
>>>>
>>>> Each of the 60 S-ATA disks sits behind a MUX card which lets it appear on both
>>>> loops.
>>>>
>>>> We could break up the shelves into two independent sets of devices which would
>>>> limit the tree depth.
>>>>
>>>> How can I get you the sysfs tree information in a useful way?
>>>>
>>> 'tree /sys/devices/'
>>> or
>>> 'find /sys/devices/'
>>> would be good.
>>>
>>> thanks,
>>>
>>> greg k-h
>>>
>>
>> Attached is the bzipped output from - the uncompressed output is quite
>> large. Note that this same server has CCIS controllers and fibre HBA's
>> as well,
>
> It's perfectly legal the way you have it, but I will say you have an
> inefficient configuration.  The way a configuration like this is
> supposed to look is that there should be a fanout expander at the top
> going to the expander in each tray, for a routing depth of two for every
> device.
>
> The way you've got it:  expander daisy chained off the next expander
> gives an unnecessary routing delay to the disks furthest away in the
> chain.
>
> James

I understand that this configuration is not optimal, but from what I saw with 
some commercial arrays, this is not an uncommon config (up to 4 shelves) when 
going for capacity over performance.

Do you have a particular SAS fanout expander in mind?  I suppose that we could 
always add more hba's as well which would have other benefits...

Thanks!

Ric