Re: RAID setup
- From: dsatchell <support@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 12 Jul 2006 02:25:01 -0700
I'm a little confused by this response. My understanding of Raid 10 (also
known as Raid 1+0) means that you have two Raid 0 set up in a mirror. I may
have these two reversed but it can also be known as Raid 01. One is a Stripe
of Mirrors and the other is a Mirror of Stripes. Either way they end up about
the same. The problem with this is that your drive efficiency is 50%, the
other 50% of which is waisted on parity (not exactly a waste), plus you then
have a hot spare (which any Raid should have so lets forget this drive).
The benefit to a good Raid controller is that you should get a 8 port if you
can afford it at all for expansion, and make sure that it has online capacity
expansion and maybe even online conversion. Then you can have two drives
(250gb ea) in a mirror and you get 250gb; add a third to Raid-5 (online
conversion) and you get 500gb; add a fourth (online expansion) and you get
750gb; all the way up to 7 drives with a hot spare.
The new popular option is Raid-6. Quoted from a Wiki: "A RAID 6 extends RAID
5 by adding an additional parity block, thus it uses block-level striping
with two parity blocks distributed across all member disks. It was not one of
the original RAID levels. Like RAID 5 the parity is distributed in stripes,
with the parity blocks in a different place in each stripe. RAID 6 is
inefficient when used with a small number of drives but as arrays become
bigger and have more drives the loss in storage capacity becomes less
important and the probability of two disks failing at once is bigger. RAID 6
provides protection against double disk failures and failures while a single
disk is rebuilding. In the case where there is only one array it makes more
sense than having a hot spare disk. The user capacity of a RAID 6 array is
n-2, where n is the total number of drives in the array."
Now make sure you check the Dell card's because a lot of theirs work where
you create a volume from all of the drives together and then you create
virtual arrays from that volume. Meaning you have a single volume of three
drives but you configure that volume as two arrays; one for your c: drive and
one for your d: drive.
What a lot of people make the mistake of at this point is that they then try
and make one array for the OS (c:), one for the data file (d:), one for the
database (e:), and then one for the pagefile (f:). This is a carry over from
the SCSI arrays where each drive letter was composed of one or more physical
drives but always a full physical drive and not part of one drive. That way
the entire drive was dedicated to one "data" funtion. But when your drive
letters are just virtual drives in a volume spread across the same physical
drives as the other drive letters, then splitting your data among multible
drive letters serves no real performance benefit.
"Jonathan Davey" wrote:
Given the last answer appears to be a bit of a show stopper and for fear of.
labouring my views, you should consider a simple high performance and high
redundancy raid 10 config, use the setup-install to create the OS, Exchange
and Data partitions.
Im no expert and know that raid setups can be quite a personal
choice/philosophy thing but I would suggest 5 identical 120Gb drives (about
the same cost your considering) plus a 6th 250Gb IDE drive.
Raid 10 the 4nr 120Gb drives and add the fith 120gb as a "self rebuilding"
hot spare.
Use the 250Gb drive as your primary backup drive.
Raid 5 is/was designed as a SCSI money saver option, Raid 10 is superior in
performance and redundancy, add to that a hotspare and you are well covered.
Indeed a Raid 10 array can survive 2 drives failing (assuming theyre not in
the same mirror set).
I think its important to appreciate and consider your time-costs and the
hardware-costs.
Oh, the 6th 250Gb IDE backup drive is just pretty usefull for fast and
efficient backups. Being on the IDE channel means its less likely to suffer
a total failure at the same time as the raid channel (card/pci slot etc) In
addition you can replace all the SATA drives and restore fast and clean from
it.
Always have an off site copy of the backup! Trying to do this with SBS
backup can be awkward, however with the BUP files as I call them neatly
sitting on a single IDE drive its easier to run a standard scheduled NT
backup to other locations/removable media etc, hell you could even put the
IDE drive in a removable caddie.
Sorry to waffle but I cant see the cost/time benefit of dual channel sata
cards..... if I had the money for dual channel sata card I would end up with
Raid 100 in any event! (Raid 10 x 10)
"ALeghart" <aleghart@xxxxxxxxx> wrote in message
news:1152551662.571324.299710@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
To run RAID 1 for your boot + RAID 5 for your data, you need a split
backplane.
The RAID controller must also accomodate a split backplane.
You should call your Dell rep. According to the "customize" options
for the PE1800, the backplane cannot be split, and the free CERC SATA
RAID controller only handles one channel.
That's why you're getting the error messages. RAID 5 must format each
drive with the same capacity. Larger drives have wasted unusable
space, and may not perform as well as factory-matched drives.
Call your Dell rep and tell him/her that the custom configuration pages
are confusing. It doesn't cost any more than doing it yourself, and
there's always a chance the rep will find you a better deal or a promo.
Regards,
Alan Leghart
mikewillard@xxxxxxxxxxxxxxxxxxxx wrote:
Hi,
I have gained a good insight into RAID setup from this group already,
and for that I thank all contributors.
I have a rather specific hardware question that will help finalise my
build spec.
I am buying a Dell PowerEdge 1800 with SATA drives, the RAID controller
is:
CERC 6 SATA RAID CONTROLLER 6 CHANNELS
My question is.. with this controller can I set up a pair of 80 gig
drives as RAID 1 for the operating system and then 3 x 250 gig drives
in RAID 5 for the data.
Wordage on the Dell site indicates that all drives must be the same
size, which is ambiguous in that the 80 gigs ARE the same size and the
3 x 250 gig drives are the same size within the scope of the RAID
setup. Does anyone have 1st hand knowledge of this controller and it
capabilities?
Thanks to anyone for info
Regards
Mike
- References:
- RAID setup
- From: mikewillard
- Re: RAID setup
- From: ALeghart
- Re: RAID setup
- From: Jonathan Davey
- RAID setup
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