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Problems with DISK capacity calculations
Hi, i need some help with understanding Hard Drives capacity calculations:
I've created RAID5 Group with 5, 146GB (not VAULT) drives - maximum logical capacity is ~534GB.
Using navicli getrg command i've checked the Logical Capacity in blocks and i got 1121115040 (which is complies with what i've created using 512B per block)
Now, when i look at the single disk capacity using navicli getdisk command i'm getting the following: Capacity: 136888 (i assume it's in MB). So doing the same RAID5 group capacity calculation using this number i get (136888 x (5-1) x 1024 x 1024) /512=1121386496
So, there is a difference of 271456 blocks, which is around 132MB.
What do i miss here? I guess the 136888 disk capacity is not the actual available capacity of this drive Does anyone know where can i get the actual numbers for disks available capacities?
Thanks
Alec
Alec2
19 Posts
0
April 13th, 2010 06:00
Thanks.
The proble is that we are trying to design automatic tool that will be able to calculate available capactiy per each raid group prior to its creation. So in order to do it we have to know what size hard drive we are using. we though to use the number get from getdisk (capacity) output.
Do you know if there is any formula that can translate this disk capacity number (from getdisk) to actual available capacity?
Thanks again
Alec
Jen_LeClair
111 Posts
1
April 13th, 2010 06:00
FLARE reserves a small amount of disk capacity for tracking tables and logs. I believe that when you are looking at the getdisk it is reporting on the disk only and not including FLARE.
A 146GB drive outside of the vault will yeild a usable capacity of 133.6473GB which matches up with the capacity of your (4+1) R-5 RAID Group.
For determining how much usable capacity you have to create LUNs look at the getRG information it is going to factor in the FLARE and the RAID Type overhead.
Jen_LeClair
111 Posts
0
April 14th, 2010 13:00
Since you are an EMC Partner there is already a disk capacity calculator available to you at the EMC Services Partner Web under "Tools & Forms" and then under "implementation services'
Mendocino
59 Posts
1
May 7th, 2010 05:00
Hi,
there is also a good document available about disk capacities and usable disk space. Can be found in the Proven Professional area:
https://community.emc.com/docs/DOC-4519 "Comparing Apples to Oranges to Bricks".
Dieter