[sclug] "Adding RAID" - what does that mean nowadays? I thought PCI bus was really slow

Tom Carbert-Allen tom at randominter.net
Wed Mar 19 22:59:01 UTC 2008

Will Dickson wrote:
>  losing a disk is a rare event, and the only point of having a RAID is 
> the amusement value and / or bragging rights.
> Will.
Your comments really shock me, RAID to me is a huge upgrade to a 
machine, much better than an extra gigahertz.

Cutting boot time in half and application loading time in half with just 
adding a couple of cheap disks sounds like money well spent to me. Much 
more worthwhile than speeding up the video rendering I might do once a 
week, because I normally do this then walk away so it's speed is not 
relevant, but loading an application is when I just want to get on with 
it and not wait.
If you edit any content of a decent size, eg larger than half your RAM, 
then you REALLY need a decent RAID strped set as your working space. Of 
course you never store data on a stripe, but they are etreamly cheap way 
of doubling or trebling the speed of common tasks for alot of people. It 
is also not uncommon to put four or eight gigabit network ports in a 
file server, which again, you won't see the benefit of without a RAID, 
which ends up being a much cheaper and less power hungry approach than 
havign multiple one gigabit single or dual disk machines, the CPU is 
never the bottleneck in fileservers afterall.

As for the stats you read about only getting 10% improvement in read 
from a mirror, this is correct for single reads. But in all servers and 
alot of desktop situations you want to read multiple files at once. In 
these test it is not uncommon to see 160% of the single drive speed in 
total. At work I have a 24 disk mirror for exactly that reason. That way 
it can saturate all it's 16 gigabit ethernet ports with video on demand 
at a sub 100ms latency (disk to screen) without dropping a frame. This 
24 disk mirror was built for under ?2500 using off the shelf parts and 
replaces what used to be 4 extreamly expensive propietary boxs....

So yeah there are MANY reasons to have RAID other than "amusement value"


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