[CentOS] Best mkfs.ext2 performance options on RAID5 in CentOS 4.2

[Sean Staats]

First of all, thanks to everybody for their responses on this thread.

On Tue, 2005-11-01 at 10:31, centos-bounces at centos.org wrote:
> Aleksandar Milivojevic <alex at milivojevic.org> wrote:
> > Correct me if I'm wrong, but you got 233MB/s for reads (the
> > block read test).
> 
> Oh, good catch!  I didn't even see that when responding (I
> assumed he could interpret the bonnie benchmark).  And if I
> see that correctly, that was with a 12GiB file (on a system
> that had 6GiB RAM).

I was fixated on the per char read rate and didn't pay much attention
to the block read rate. ;-)

> > Assuming your disks can do 50MB/s sustained transfer rate
> > each, you are preatty darn close to the theoretical maximum
> > of (6 - 1) * 50MB/s = 250MB/s for 6 disk RAID5.

At least the read speeds are performing as can be reasonably expected
for this particular configuration.  I am certainly happy with that
result.

> On reads, yes.  3Ware is clearly leveraging the ASIC's
> non-blocking I/O for reads from RAID-5, which basically act
> like RAID-0.
> 
> > RAID5 as such is bad choice for file systems that will have
> > more than about 30% of writes (out of total I/O).
> 
> He still should be seeing at least 100MBps for RAID-5 writes
> on a 3Ware Escalade 9500S with 6-discs (180MBps is about the
> maximum for RAID-5 writes on the 9500S' ASIC with DRAM).  The
> ASIC is fairly good at sequential writes to RAID-5, and there
> is enough DRAM to buffer all but the heaviest of random I/O.
> 
> Still, the new 9550SX series has a PowerPC.  AMCC's influence
> is clearly being pressed on their 3Ware acquisition, as they
> are _the_ company for the IBM embedded PowerPC 400 line now. 
> The 9550SX is supposed to be cable of 380MBps for RAID-5
> writes -- double the 9500S best benchmarks.
> 
> > If most of the I/O will be writes, and you care about 
> > performance, you should use RAID-10.
> 
> Yep, mega-dittos on that point.
> 
> > Remember, writes to Dumb, not-optimized RAID5
> > implementation is slower than writing to a single 
> > disk. This is generic RAID wisdom, nothing to do with
> > any particular implementation. In the worst case scenario,
> > the write operation on 6-disk RAID5 volume involves
> > reading a data block from 5 drives, calculating XOR,
> > and writing back one block of data and one block of
> > checksum.  Whichever way you do it, it ain't gonna be
> > fast.
> 
> Still, he shouldn't be seeing less than 100MBps writes on the
> 3Ware Escalade 9500S series with its on-board ASIC and DRAM
> buffer.

I'm going to upgrade the firmware to the latest revision which should
improve the write performance.

> At least the reads are very accurate for his configuration. 
> I'm curious how he is striping though?  It might have been
> better to do a 12-disc RAID-5 and get close to 400MBps reads.
> 
> Or if performance was more important than efficiency, making
> one 6-disc volume RAID-10 would give close to 300MBps reads,
> 150MBps writes -- maybe higher.

I'm sticking with RAID-5 to maximize storage space while having some level of
protection against drive failure.

Cheers!
-Sean