Hard disk bottle neck.

Bill Moran wmoran at potentialtech.com
Sun Sep 28 13:54:39 UTC 2008

"Danny Do" <danhdo at gmail.com> wrote:
> Hi guys,
> I have this problem for years but couldn't find a way to solve it.
> I have a file server handling large files from 1MByte to 1GByte. 
> Server Info:
> FreeBSD 6.2 
> Apache 2.2.9
> DELL PowerEdge 1850
> 2GB RAM (only 184MB is active)
> 6x300MB SCSI 10K RPM RAID5
> Gigabit Ethernet Connection
> My server can output NO MORE than 60Mbps (read only). 
> The bottle neck is the hard disk.

What evidence do you have that the bottleneck is disk IO?  I've seen no
evidence, only speculation.

In addition to the advice of others, you may be able to just beef up the
RAM.  2G isn't much these days.  If you've got 200M active, you've got
about 1.8G available to cache files.  If you have repeated access of the
same file, the OS can cache that file data and not even use the disk, but
it can only do that if it has enough RAM to work with.  You need to get
your facts straight, though.  According to the specs you've got above,
you've only got 1.5G of disk.  I expect you meant 300G disks.

You could also add disks in a RAID 10, which is generally faster than
RAID 5, or move to 15,000 RPM disks.  I think you might be surprised how
much adding some RAM will help, though, unless your access patterns are
very random, RAM should speed up the access of popular data significantly.

Bill Moran

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