Watching performance on a DHCP Server

Simon Hobson dhcp1 at
Wed Feb 13 20:04:39 UTC 2008

Frank Bulk wrote:

>How much of a performance advantage would be gained with fsync just by using
>a SCSI or serial ATA flash disk, or a USB thumb drive?

Compared with a single hard drive - a LOT

Compared with a raid controller with caching enabled - not as much 
but it depends what else is going on.

If the DHCP writes were the only thing going on, then the raid 
controller cache effectively gives you a drive with the same 
performance as a ram disk. If the disk system is very busy then it's 
not as clear cut as the write may still need to wait for physical 
accesses to complete before a place in the cache can be made for it.

However, you would not want to use just any old flash for this, older 
flash has a very finite limit to write cycles and can quickly become 
useless when storing a busy filesystem. Some newer flash technologies 
have eliminated this issue.

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