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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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.
This email and its contents may be confidential. If it is and you are not the intended recipient, please do not disclose or use the information within this email or its attachments. If you have received this email in error, please delete it immediately. Thank you.
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Antonio Varni -
jeff.mery＠ni.com -
Timothy Sesow