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Storage Array Availability Calculation Tool - BackGrounD Software - ©2007 All Rights Reserved.
Enter information about the physical disk device inside the array:
Disk MTBF: hrs. This means that if you ran this many disks (as stated above) at the same time, one disk would fail each hour, 24 would fail each day, and 365 would fail each year.

Historical rates:
1993 100,000-250,000
1999 400,000
2002 600,000-800,000
2007 1,200,000

MTTR: hrs

Typical MTTR Rates:
Platinum Support
Support on-site, spares on-site: 1 hr
Support on-site, spares off-site: 4 hrs
Gold Support
Support off-site, spares off-site: 8 - 16 hrs
Silver Support
Support off-site, spares off-site: 24 - 48 hrs
Bronze Support or Warranty Only
Support off-site, spares off-site: 72 - 168 hrs

Annual Failure Rate:
Reliability:
Annual Failure Repair Rate:
Disk Availability: %
Expected disk failure rate in a 14 disk storage sub-system: daily or
annually.
(considering past burn-in period and pre end-of-service-life period)
 
For details and formulae, please see whitepaper:
Maximum Achievable Storage Array System Availability
LEGEND:Availability (%)Allowed Down Time (minutes per year)
Highly Available (HA)
A > 99.9999% (six nines) DT < 0.5
99.999% < A < 99.9999% (five nines) 0.5 < DT < 5.26
Non HA
99.99% <= A < 99.999% (four nines) 5.26 < DT < 52.5
99.9% <= A < 99.99% (three nines) 52.5 < DT < 525
A < 99.9% (less than three nines) DT > 525
RAID Groups
RAID 0 Striping across all disks No Data Redundancy
RAID 1 Mirroring each disk to it's pair Full Data Redundancy
RAID 0+1 Striping across all disks, then mirroring Full Data Redundancy
RAID 5 Distributed data parity Full Distributed Data Redundancy
RAID 10 Mirroring each disk to it's pair, then striping Full Data Redundancy
This will be your storage solution availability for selected number of disks in a RAID and type of RAID
Without Hot Spare
# of disks RAID 0 RAID 1 RAID 0+1 RAID 5 RAID 10
2
 % % - - -
3
 % - - % -
4
 % % % % %
5
 % - - % -
6
 % % % % %
7
 % - - % -
8
 % % % % %
9
 % - - % -
10
 % % % % %
11
 % - - % -
12
 % % % % %
13
 % - - % -
14
 % % % % %
 
With Hot Spare
# of disks RAID 0 RAID 1 RAID 0+1 RAID 5 RAID 10
2
 % % - - -
3
 % - - % -
4
 % % % % %
5
 % - - % -
6
 % % % % %
7
 % - - % -
8
 % % % % %
9
 % - - % -
10
 % % % % %
11
 % - - % -
12
 % % % % %
13
 % - - % -
14
 - - - - -
 
With 2 Hot Spares
# of disks RAID 0 RAID 1 RAID 0+1 RAID 5 RAID 10
2
 % % - - -
3
 % - - % -
4
 % % % % %
5
 % - - % -
6
 % % % % %
7
 % - - % -
8
 % % % % %
9
 % - - % -
10
 % % % % %
11
 % - - % -
12
 % % % % %
13
 - - - - -
14
 - - - - -
 

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