1GB FBWC has slower reading speed than 512MB BBWC?

[smartynaoki]

I found that 1GB FBWC is much slower than 512 BBWC in random read test. That's quite strange. Do anyone know the reason?

Hardware:

CPU: Xeon L5520 x 2

Memory: 72GB

RAID: 300G x 1 RAID 0, 600G x 7 RAID 5

OS: CentOS 6.4 64bit

RAID Controller: Smart Array P410 with 6.00-2 Firmware

 Tool:

fio

Options:

 -direct=1 -iodepth 16 -thread -rw=randread -ioengine=psync -bs=16k -size=20G -numjobs=10 -runtime=200 -group_reporting -name=mytes

Test target:

The second logical volume(600G x 7 RAID 5).

Result:

                IOPS    Bandwidth(KB/S)
P410 1G FBWC    461     7,383
P410 512M BBWC  1,276   20,426

And I also did randwrite/read/write test. In all other tests, 1G FBWC is faster than 512M BBWC.

[Dennis Handly]

>I found that 1GB FBWC is much slower than 512 BBWC in random read test.

I would have thought if you have truly random reads the cache won't help.

And if you do have a larger cache, it shouldn't take that much longer to determine it isn't there.

[David_Tocker]

Firmware/drivers? Otherwise try some real workloads, sometimes the SA optimizations do bad things to synthetic benchmarks but work better in real workloads. Either result seems relatively quick.