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тАО07-02-2010 03:23 AM
тАО07-02-2010 03:23 AM
I have a basic query on EVA space. Pls help me understand this.
Let us consider an EVA 4000 2C4D array with 56 x 300 GB disks. Allocation Alarm Level in the Default Disk Group (the only Disk Group) is 95%.
In this case,
Raw capacity = 56 x 300 GB = 16800 GB
Formatted capacity = 56 x 279.39 GB = 15645.84 GB
In StorageWorks CvEVA > EVA Storage Network Properties, under Managed Storage System Capacity,
Total = 15083 GB <- where's 562.84 GB
Suppose 13736 GB is already allocated
Then, remaining 1346 GB <- must be Vraid0
If it is Vraid5, maximum size of the Vdisk is 1076 GB (which is about 80% of Vraid0 disk)
My concern is - without triggering the Allocation Alarm, what is the maximum size that we can allocate to a new Vdisk. Here's my workout:-
95% of 15083 GB = 14328.85 GB
Already allocated (in this case) = 13736 GB
So, max allowable Vraid0 disk size = (14328.85 - 13736) = 592.85 GB
If we want a new Vraid5 disk, its maximum capacity can be 80% of 592.85 GB = 474.28 GB
Pls correct me if I am wrong.
Solved! Go to Solution.
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тАО07-02-2010 03:42 AM
тАО07-02-2010 03:42 AM
SolutionSo you have (56 - 2)x 279.39 GB = 15087 GB available for vdisks. 95% of that is 14332.
A vdisk in RAID 5 takes a 25% more space than in RAID 0 (EVA uses 4 data + 1 parity).
So your calculations are correct, yes.
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тАО07-02-2010 04:03 AM
тАО07-02-2010 04:03 AM
Re: EVA // Remaining space & Allocation Alarm Level
Can you also pls let me know if disk space reservation in case of Disk Drive Failure Protection set to None & Double ... are 0 and 4 respectively.
EVA uses 4 data + 1 parity << pls clarify this part
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тАО07-02-2010 04:21 AM
тАО07-02-2010 04:21 AM
Re: EVA // Remaining space & Allocation Alarm Level
And level double does indeed reserves 4 times the size of the largest disk drive in the group.
4D+1P indicates how the EVA does VRAID-5 redundancy. It takes 4 Data chunks, calculates the Parity chunk and stores all five chunks on five different disk drives in the group so that any one disk drive can fail, but you do not have lost data.
Well, at the low level it is a bit more complex, but the basic rule is 4D+1P on five different physical disk drives.
Do not confuse the "5" in VRAID-5 with the "5" in "five disk drives". They are not related.
Other arrays do a RAID-5 with 3D+1P or 7D+1P or other values.
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тАО07-02-2010 05:04 AM
тАО07-02-2010 05:04 AM