I have a storage unit with 2 backplanes. One backplane holds 24 disks, one backplane holds 12 disks. Each backplane is independently connected to a SFF-8087 port (4 channel/12Gbit) to the raid card.

Here is where my question really comes in. Can or how easily can a backplane be overloaded? All the disks in the machine are WD RE4 WD1003FBYX (black) drives that have average writes at 115MB/sec and average read of 125 MB/sec

I know things would vary based on the raid or filesystem we put on top of that but it seems to be that a 24 disk backplane with only one SFF-8087 connector should be able to overload the bus to a point that might actually slow it down?

Based on my math, if I had a RAID0 across all 24 disks and asked for a large file, I should, in theory should get 24*115 MB/sec wich translates to 22.08 GBit/sec of total throughput.

Either I'm confused or this backplane is horribly designed, at least in a perfomance environment.

I'm looking at switching to a model where each drive has it's own channel from the backplane (and new HBA's or raid card).

EDIT: more details

We have used both pure linux (centos), open solaris, software raid, hardware raid, EXT3/4, ZFS.

Here are some examples using bonnie++

4 Disk RAID-0, ZFS

WRITE     CPU    RE-WRITE  CPU    READ      CPU    RND-SEEKS
194MB/s   19%    92MB/s    11%    200MB/s   8%     310/sec  
194MB/s   19%    93MB/s    11%    201MB/s   8%     312/sec  
--------- ----   --------- ----   --------- ----   ---------
389MB/s   19%    186MB/s   11%    402MB/s   8%     311/sec

8 Disk RAID-0, ZFS

WRITE     CPU    RE-WRITE  CPU    READ      CPU    RND-SEEKS
324MB/s   32%    164MB/s   19%    346MB/s   13%    466/sec  
324MB/s   32%    164MB/s   19%    348MB/s   14%    465/sec  
--------- ----   --------- ----   --------- ----   ---------
648MB/s   32%    328MB/s   19%    694MB/s   13%    465/sec

12 Disk RAID-0, ZFS

WRITE     CPU    RE-WRITE  CPU    READ      CPU    RND-SEEKS
377MB/s   38%    191MB/s   22%    429MB/s   17%    537/sec  
376MB/s   38%    191MB/s   22%    427MB/s   17%    546/sec  
--------- ----   --------- ----   --------- ----   ---------
753MB/s   38%    382MB/s   22%    857MB/s   17%    541/sec

Now 16 Disk RAID-0, it's gets interesting

WRITE     CPU    RE-WRITE  CPU    READ      CPU    RND-SEEKS
359MB/s   34%    186MB/s   22%    407MB/s   18%    1397/sec 
358MB/s   33%    186MB/s   22%    407MB/s   18%    1340/sec 
--------- ----   --------- ----   --------- ----   ---------
717MB/s   33%    373MB/s   22%    814MB/s   18%    1368/sec

20 Disk RAID-0, ZFS

WRITE     CPU    RE-WRITE  CPU    READ      CPU    RND-SEEKS
371MB/s   37%    188MB/s   22%    450MB/s   19%    775/sec  
370MB/s   37%    188MB/s   22%    447MB/s   19%    797/sec  
--------- ----   --------- ----   --------- ----   ---------
741MB/s   37%    376MB/s   22%    898MB/s   19%    786/sec

24 Disk RAID-1, ZFS

WRITE     CPU    RE-WRITE  CPU    READ      CPU    RND-SEEKS
347MB/s   34%    193MB/s   22%    447MB/s   19%    907/sec  
347MB/s   34%    192MB/s   23%    446MB/s   19%    933/sec  
--------- ----   --------- ----   --------- ----   ---------
694MB/s   34%    386MB/s   22%    894MB/s   19%    920/sec

28 Disk RAID-0, ZFS

32 Disk RAID-0, ZFS

36 Disk RAID-0, ZFS

More details:

Here is the exact unit:

http://www.supermicro.com/products/chassis/4U/847/SC847E1-R1400U.cfm