[LUNI] Need help determining what's causing a server to be slow - SOLVED

[Branko Kotur]

Just wanted to update anyone in case this came up again in some obscure way.  
I had initially disabled write caching since the RAID card complained that I 
could lose data since I didn't have a Battery Backup Unit installed on the 
card.  I wanted to be safe rather then sorry even though there were UPS's for 
the servers.  After enabling write caching and doing some tests, the problems 
pretty much disappeared and the servers are now operating at their full 
potential.  

On Monday 04 December 2006 1:26 pm, Branko Kotur wrote:
> I've recently put together 2 new servers to replace older existing ones.
> However, whenever these new servers do any kind of disk intensive access,
> they seem to fall flat on their faces to the point where they're at times
> unresponsive (for example, untarring a 1GB tar file).  The only thing I can
> think of is that something isn't configured right as they should basically
> blow away the older servers that I'm using.  Even doing a simple operation
> like ls in a director that only had 10 files takes forever.
>
> Whenever I've noticed the unresponsiveness, the load tends to be around 4 -
> 8 with the IO Wait (as reported by top) is anywhere from 80% - 100% for 1
> or both CPU's.  I'm wondering if the bottleneck is the RAID card or the
> driver for the card.  I'm also wondering if the PCI-X slot (that the RAID
> card is plugged into) may be the bottleneck.
>
> Some info on these servers:
>
> Dual core Opteron 180, 4GB RAM, 3ware 9550SX RAID card, CentOS 4.4 64bit,
> WD 2 Caviar RE SATA 3.0G/s drive in RAID 1, Supermicro H8SSL-i motherboard.
>
> CentOS 4.4 comes with the 3ware drivers as part of the install CD so I
> didn't think I needed to install them separately.  However, the actual file
> is much smaller then the one provided by 3ware (53K as opposed to the 313K
> version offered by 3ware).  Is the included one just a basic driver?  3ware
> seems to offer open source drivers, so I don't see why the included one
> would be any different then the official one.
>
> When I do an hdparm -tT /dev/sda, the results look pretty good (at least
> compared to the IDE drives I've been using).  However, this is my first
> time using SATA drives, so I don't have anything to compare with.  If
> anyone has any SATA drives, can you let me know if these results are good
> or bad?
>
> /dev/sda:
> Timing cached reads: 3772 MB in 2.00 seconds = 1884.40 MB/sec
> Timing buffered disk reads: 190 MB in 3.00 seconds = 63.26 MB/sec
>
> I've used 3wares' 3DM2 utility to set the RAID card to performance mode,
> but that doesn't seem to have helped much, if any.  I'm also wondering if
> the PCI-X slot is the bottleneck.  I'm pretty sure it can't do the full
> 3.0Gb/s, but I would think it can come close.
>
> Any thoughts or ideas that I can look into?  Right now, my 3 year old
> servers with IDE drives and software RAID are out performing the new
> servers when under load or doing heavy disk access.  I know they can do
> better, but I just can't seem to find out what the problem is.