Re: OT: Kaliedascape Wannabe!!

["Paul Bendall" <paul@xxxxxxxxxxxxxxxxx>]

Simon,

Quite a few questions to answer.

Firstly I would try to decide if you want a rackmount disk=20
enclosure, like this 4 disk system from Scan.Com:

http://www.span.com/catalog/product_info.php?
cPath=3D18_2003_1703&products_id=3D13942

Or, as the price is quite close to that of some of the NAS solutions=20
you could get these instead and use it as Network Attached Storage=20
with is seperate to the system you are building:
Synology - http://www.synology.com/enu/products/RS407/index.php

Thecus - http://www.thecus.com/products_over.php?
cid=3D12&pid=3D26&PHPSESSID=3D1a210621d77bdebf057eb58f73082165

ReadyNAS - http://www.netgear.com/Products/Storage/ReadyNAS1100.aspx

QNAP - http://www.qnap.com/pro_detail_feature.asp?p_id=3D71

RAID is fairly simple and certainly at the four disk level:
RAID 0 - No fault tolerance and disk read / writes are spread across=20
all four disks (therefore 4 times faster than a single disk).=20
However, you are four times more likely to have a failure as a=20
single disk failing will fail the entire array.

RAID 1 - Is referred to as mirroing and needs two disks, each write=20
is written to both disk at the same time therefore if one disk fails=20
te other takes over. In a four disk system you would have two=20
separate mirrors (50% of your disk space is useable)

RAID 5 - Most likely configuration in a four disk system. Disk=20
writes are written across three disks and the fourth disk is used to=20
generate a parity (which means if any one disk fails the data is not=20
lost because it can be calculated from the parity disk). This is=20
slightly simplistic as RAID 5 is distributed parity which means the=20
parity could be on any one of the disks not on a single dedicated=20
disk. Read performance is excellent as data is coming from three=20
disks, write performance is better than a single disk but not as=20
good as 3 disks because calculatting the parity degardes performance=20
slightly (however you have fault-tolerance and you are able so use=20
75% of total size of the disks)=20

JBoD - Just a bunch of disks is not really RAID but you may find it=20
mentioned. It means the disks are just individual disks and you=20
would see them individually in the operating system.

Also don't forget when talking about RAID the interface that the=20
system uses. RAID used to be possible only with expensive SCSI disks=20
and controllers. However, with the advent of the SATA interface it=20
is now much cheaper.

HTH

Paul

--- In ukha_d@xxxxxxx, "simon.millward"
<simon.millward@...>=20
wrote:
>
> Hi guys, It's been a while since I last posted on this site, so I=20
> would like to say hello to everyone again.
>=20
> I have a question that I am hoping someone can help me with. I=20
> recently looked into purchasing the basic Kaliedscape 3U version,=20
> until SWMBO saw the hefty =A314K price tag and asked me if I could=20
> build something cheaper. So that's my project now!!!
>=20
> So I must ask some questions of all the helpful souls out there.
>=20
> 1. I need a 19" Rackmount Sever Case that I can use as a NAS.
I=20
have=20
> looked around but can only find some that don't really suit. I saw=20
> one like http://www.raidware.com/chassis.htm
the 3U unit. I am=20
> preferably after vertical mount hot swap drives.
>=20
> 2. I would like to be able to keep adding drives and it be able to=20
> slot right in.
>=20
> 3. If I then decide to build another server, I would like it to be=20
> able to cluster them.
>=20
> I must apologise for this post but when it comes to RAID I get a=20
> little confused. Also apologies if this sounds too much like the=20
> Kaliedascape version, but it is a brilliant idea just too=20
expensive!!
>



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