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SabarnaDeb
2 Intern
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139 Posts
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May 28th, 2014 05:00
CX4 240 - Getting different "User Capacity" in thin pool VP...
Hi All,
In one of the thin pool (lets say thin pool0), first we added five 1834.354GB(formatted size) SATA HDD (4 for data and 1 for parity in raid group) and second time, we added four 1834.354GB(formatted size) SATA HDD (3 for data and 1 for parity in raid group) in same enclosure (lets assume Enclosure 1) And third time, we added eight 2751.527GB(Formatted size) SATA HDD (7 for data and 1 for parity in raid group) in same "thin pool0" but in different Enclosure (Lets assume Enclosure2). Then as per my calculation, we should get -> 4 * 1834.354 + 3 * 1834.354 + 7 * 2751.527 = 31.34 TB user capacity but in Unisphere, it is showing 28.64TB User Capacity. There is 2.7TB difference. Can anyone tell me where 2.7TB used? Correct me if i am wrong......Looking forward for reply...thanks
823
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Posted May 29th, 2014 01:00
The first defines the default disk count. The algorithm would try to match the configuration whenever you add disks. if the count is not as first one. Then it will split them as two internal raid groups. And it has the overhead as well, so you got 28.64 TB
Please look the below table.
Total Disks added Data disks Parity Disks Usable Cap / Disk (GB) Total usabe data disk capacity (GB) 5 4 1 1,834.35 7,337.42 4 3 1 1,834.35 5,503.06 8 4 1 2,751.5311,006.11 2 1 2,751.535,503.05 Total (GB) 29,349.64 823
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Posted May 29th, 2014 05:00
Hi Sabrana,
You didn’t mention which Raid Protection you choose while adding 8 drives? With 8 drives in one go you can either select R6 (6 Data Drive + 2 Parity Drive) or R1/0 (4 data drive and 4 mirror drives).
Based on above you can calculate your user capacity.
A rough formula for user capacity should be:
User Capacity = Raw disk capacity minus overhead (Raid Overhead and mapping overhead)
Regards,
Vivek
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Posted May 29th, 2014 08:00
Please see the attached best practice guide - look at page 65 for the best practice guidelines for creating pools. The previous notes for others have mostly answered your question about capacity, but you really should review the best practices for Pools for creating the initial Pool and for when you add more disks to the pool. If you are using SATA disks, you should be creating a Raid 6 type and the number of disks that you add should be multiples of 8 (6+2). If you do use a Raid 5, then you should only use multiples of 5 (4+1). Any other number of disks will potentially cause performance issues.
There are other White Papers available on support.emc.com about Virtual Provisioning under the CLARiiON CX4-Series documents section. You should take a look at the others concerning Virtual Provisioning and FAST VP. Taking the time to design your Pools before you create them will be beneficial in the long run.
Create Pools that match the types of usage.
glen
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Posted June 25th, 2014 07:00
Thanks Glen
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Posted June 25th, 2014 07:00
Raid5 only
823
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Posted June 25th, 2014 07:00
Thanks buddy....i want to know - is there any possibilities to remove the these added disks with any disruption so that i will create new Thin pool with additional 7 new SATA drives (14 +1 )..??
823
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Posted July 11th, 2014 01:00
Sorry typing mistake. Is there any possibilities to remove these added disks without* any disruption so that i will create new Thin pool with additional 7 new SATA drives (14 +1 )..or (7+1) ??
823
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Posted July 11th, 2014 04:00
nope, can't remove drives from an existing pool..entire pool has to be destroyed.
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Posted July 11th, 2014 22:00
Yes dynamox , I got the same answer from EMC too. Thanks………
Regards,
Sabarna Deb
“skill, will and hill”
Roger_Wu
6 Operator
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4025 Posts
823
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Posted May 29th, 2014 00:00
The fixed overhead of thin LUNs should be 3GB, the variable overhead is equal to 3% of the LUN's user capacity. Do you make sure the RAID layout is the same as what you mentioned?