Linux-PowerEdge Digest, Vol 68, Issue 35

Alexander Dupuy alex.dupuy at
Wed Feb 10 15:26:51 CST 2010

John Heim writes:
> I hope this is not too far off topic (maybe its considered on topic [I 
> hope]).

Makes a nice change from the "third-party drives" thread :-)

> I think we can get a machine with a quad core, 32 Gb of RAM, and 300 Gb disk 
> for under $6000. But I'm confused about disk. I would think disk speed 
> would be fairly important. How can I configure a machine with a fast disk? 
> What are my options from Dell in that regard?

You want to get fast disks, be sure to get the 15K RPM models - these 
have the least rotational latency, and given equal recording technology, 
should be able to pull more bits off the drive in the same amount of time.

You might also want to look at getting a hardware RAID card or 
daughterboard like the PERC-6i - these will allow you to set up a 
RAID-10/50/60 that will stripe all data between two drives, giving you 
another twofold speed increase. You probably want to make sure that your 
card has battery backup if you care about your database - otherwise a 
power cut can lose cached data rather painfully, even if you have a UPS. 
If you're moderately paranoid, or your data is important, you should 
disable on-drive write caching, as these never have battery backup - but 
this will cost you some speed. (This is a software issue, though, and 
won't affect your purchased configuration.)

If you have the budget for it, look at putting the database write-ahead 
log on an SSD "flash drive" for an extra speed boost. If not, another 
possibility might be to restrict write-back caching from the RAID card 
to a single (logical) disk, and put the write-ahead log on that disk, 
with the rest of the drives in write-through mode, although I can't say 
for sure whether that will really keep the cache reserved for the log. 
You can also put the filesystem journals on the SSD or cached disk 
(don't do this for the root/usr filesystems, but others are okay) - this 
will speed up filesystem writes as well (although possibly not for the 


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