We noticed this about 2 years ago and
came up with almost exactly the same number you did. Your calculation
results in ~56% usable space per disk. We use a slightly smaller
snap reserve which gives us ~60% usable space per disk.
I have to agree with your statement
about doing your own calculations. Organizations are going to have
differing standards for the number/size of RAID groups, number of hot spares,
size of snap reserve, etc. As long as they truely are *standards*
then estimated disks needed for growth becomes a fairly simple calculation.
Jeff Mery, MCP
National Instruments
-------------------------------------------------------------------------
"Allow me to extol the virtues of the Net Fairy, and of all the fantastic
dorks that make the nice packets go from here to there. Amen."
TB - Penny Arcade
-------------------------------------------------------------------------
Antonio Varni <avarni@cj.com> Sent by: owner-toasters@mathworks.com
05/12/2004 12:10 PM
To
Timothy Sesow <tsesow@nsllc.com>
cc
Jack Lyons <jack.lyons@martinagency.com>,
toasters@mathworks.com
Subject
RE: Size calculations
It's suprising how much usable space you really end
up with.
For example, one of my filers has a single volume spanning 3 raid groups.
Each raid group is composed of 12 data disks and 1 parity disk.
That's 13x3= 39 144 'gig' drives.
In 1024*1024*1024 gigs, that's ~133.9gb per drive -- or about 5221
gigs of
raw storage.
5221
-401 (parity drives)
------
4820
*0.9 (~WAFL overhead)
-----
4338
*0.8 (Assuming 20% snap reserve)
-----
3470
*0.85 (NetApp says you should not use more then ~85% of your usable space
or you might start seeing sharp performance declines).
-------
2949 gigs usable.
It's always good to do your own calculations before buying so you
make sure you end up with enough usable space.
On Wed, 12 May 2004, Timothy Sesow wrote:
> Disk manufacturers use decimal-based numbers for disk sizes, so that
a
> 146GByte drive is 146*1000*1000*1000 bytes. I have heard that
this is
> due to legal requirements, but I am not a lawyer.
>
> Most software, including DataONTAP, uses 1024*1024*1024 to mean a
> Gigabyte.
> So a 146Gbyte disk drive (146*1000*1000*1000) is actually 136GBytes
of
> usable disk space.
>
> My impression is that NetApp is one of the few vendors who are actually
> straight forward about this. On their quotes for new systems,
they have
> a field for "usable space", which is based on 1024*1024*1024
> calculations AND they deduct for snapshots.
>
> Tim Sesow
> VP Engineering
> 303-948-3360
> cell 303-809-8070
>
> -----Original Message-----
> From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com]
> On Behalf Of Jack Lyons
> Sent: Wednesday, May 12, 2004 8:26 AM
> To: 'toasters@mathworks.com'
> Subject: Size calculations
>
> Can you tell me whether or not a TB = 1000 GB or 1024 GB
> In my volume properties screen:
>
> Used Capacity: 1.18 TB
> % Used: 90%
> Total Capacity: 1.31 TB
>
>
> But in my Manage Volumes screen it shows I have 127 GB available.
> 1.31 - 1.18 = .13 TB = 133.12 GB if 1 TB = 1024 GB
> 1.31 - 1.18 = .13 TB = 130 GB if 1 TB = 1000 GB
>
> 127 GB = .127 TB if TB = 1000 GB
> 127 GB = .130 TB if TB = 1024 GB
>
> so it seems that in one screen they use 1 conversion factor and another
> screen they use a different one.
>
>
>
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