SUMMARY : SSA question

From: Rahul Roy (
Date: Tue Oct 01 1996 - 13:28:19 CDT

My original query :

Hi managers !!

H/W : Sun Ultra 170E, 256 Mb RAM, Token Ring, SSA Model 1010 w/ fiber channel
      Solaris 2.5

I need to add 2.1 Gb x 12 disks to an existing array of 2.1 Gb x 6 disks
The question I had is that would it be worthwhile to add a second fiber
channel from a performance perspective ?? This array is mostly used for
NFS mounting users directories and various application software.

Got a total of 3 responses :

Charlie Clelland <>
Ray Trzaska <>
Bill Krauss <billk@LANcomp.COM>

I was advised not to put in a second channel, primarily because the array
controller is built to support approximately 18 Mb/s of sustained
throughput...which is way beyond the throughput sustained by a Token Ring
network - not matter how good it may be !!!!!

The complete responses follow :

Provided you are spreading the disks across all the scsi chains in the box
and your partitions are set up so that each partition is spread across
the maximum number of chains another FC probably won't help much.
The capacity of a single fibre channel seems to be adequate to handle even
a fully populated SSA. A few points:

- make sure you are using the latest revisions of the fibre channel and
controller firmware, the latest controller firmware is supposed to give
a significant improvement in throughput.
- use the analysis tool in vxva to determine the hits and average service
times, if your partition arrangement is sub-optimal you'll see a dramatic
increase in average service time as the request rate increases - RAID5
shows this effect at relatively low request rates rates.
- you don't indicate the volume types or sizes you are using - our experience
with SSAs indicates that RAID5 is only useful for low request rates, if you
have volumes which get hit hard consider striping across a number of disks
with a striped mirror.
- don't use small partitions - anything less than 2G incurs too large an
overhead from the volume manager - the overhead is much higher than that
on scsi disks.


Charlie Clelland

don't do it.
the second optic module on the storage array is for host
sharing/dual attach to allow disks to be shared over hosts.

the throughput on the optic cabling/io controlers is able
to cope with a fully laden SSA, even when reasonably striped.

single host/single SSA/fual optic cable will mean that you would see
all the disks twice, and you will be into volume reservation games
againt yourself.


I'm guessing that your real question is whether you should add a second
array or not. The second Fiber Channel connector on the SSA 101 is for
dual homing the array. I don't believe that the Fiber Channel would be a
bottleneck in this case. (A properly tuned array can sustain > 18 MB/s.
Even switched FastEthernet would bottleneck at 12.5 MB/s ath that
particular host's adapter.)

I don't think that you can configure the second Fiber Channel on the same
host. Let me know if you've heard differently.

Bill Krauss

regards and thanks to all,


Rahul Roy Voice: (609) 727-4600 Ext.2650
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