This article intends to help the readers to quickly understand what Virtual Provisioning is on VNX by providing the 12 FAQs.

Q1: What is virtual provisioning on VNX?

A1: Virtual Provisioning is a software feature running on VNX. It features pool-based storage layout. As compared with traditional RAID Group, Virtual Provisioning simplifies storage provisioning and management. You can add a large number of disks into a pool (a RAID-Group only supports 16 disks in total) and create pool-based LUN. Virtual Provisioning also provides ThinLUN capability to increase storage utilization and accommodate the dynamic changes on storage capacities.

Q2: Does this feature need a license?

A2: Virtual Provisioning is initially introduced as a licensed feature on CLARiiON FLARE Release 28.5. After FLARE Release 30, this feature is for free. You just need to install the virtual provisioning enabler to enjoy it. Please refer to emc246225.

Q3: Does all the virtual provisioning version has the same features? Is there any change along the version path?

A3: No. Virtual Provisioning is implemented through a phased manner. At FLARE Release 28.5, only ThinLUN is supported. As of FLARE 04.29.000.5.016, it began to support MirrorView and SANCopy with some of the Limits being increased. At FLARE 30, ThickLUN was introduced. Before 04.30.000.5.522, lots of features like LUN expand and shrink, Tiering preference, RAID1/0 support, etc. were added. In the latest version of the next generation VNX (MCx), ThinLUN is now the default LUN type when you create a pool LUN. Please refer to the specific virtual provisioning release notes for new features and changes.

Q4: What is pool, ThinLUN, ThickLUN and slice?

A4: Just consider pool as a really big RAID Group. It is a container for disks management. ThinLUN and ThickLUN are the two LUN types supported by pool. ThinLUN is capable of overprovisioning because it only consume physical storage when new writes incoming in. ThinLUN doesn’t allocate all of the physical capacity at creation. Although ThinLUN features of consumed-on-demand storage, but there will be performance overhead for internal storage layout management. To complement this, ThickLUN was introduced. It has much less performance overhead as compared with ThinLUN and inherits the same ease of use characteristic from pool. But ThickLUN do not provide consumed-on-demand capability. Slice is an internal data structure for storage allocation. End users do not have control on slice.

Q5: What’s the difference between classic LUN, ThinLUN and ThickLUN?

A5: Please refer to emc298558. A detailed comparison table will show you all the information.

Q6: What is the size of a single slice?

A6: Before MCx Release 33, it was 1GB. For MCx and later, it is 256MB.

Q7: Can we reclaim the disks in a pool?

A7: No, you cannot. Delete the pool is only way to release the disks. Please refer to emc316137.

Q8: Is Pool or Pool LUN expansion disruptive?

A8: No, both are non-disruptive operation.

Q9: How to maximize storage utilization of a pool. Is there any recommendation?

A9: RAID 5 does it better than RAID/10/6 for the same number disks as usual. Typically, virtual provisioning software creates 4+1 private RAID Group for RAID5 pool before FLARE Release 32. Actually, when you add 7 drives into a pool, it will create a 6+1 RAID Group. So add 7 disks into a pool at one time can maximize the storage utilization. For FLARE Release 32 and later, new 8+1 RAID5 type is now supported for a single tier. Please refer to emc256066 for more details.

Q1: How to resolve pool LUN performance issue?

A1: Please refer to emc297178 for the best practices.

Q11: Can we shrink a pool LUN?

A11: Yes, but only Windows server 2008/2012 and VMware VMFS 5 support this feature. An example for Windows Server 2008 can be found at https://support.emc.com/kb/12925.

Q12: Do we have recommend number of disk configuration for a pool?

A12: Before FLARE Release 32, we would recommend configure 4+1/6+2/4+4 separately for RAID5/6/10; For Flare Release 32 and later, we would recommend configure  4+1 or 8+1/6+2 or 14+2/4+4 separately for RAID5/6/10. TAs we can see, two new types are added for better storage capacity utilization.

                                                                                     

Author: Steve Zhou

             

iEMC APJ

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