VMworld 2015: Flash Storage Best Practices #STO6326-SPO

Cody & Ravi from Pure Storage brought a good deep-dive of all-flash storage in a virtual (VMware) world. Major emphasis on “deep-dive” as they went into the nitty-gritty of VAAI primitives and especially SCSI UNMAP across the versions.

The only weak spot was the age-old issue of having to cram too much content into too little time. They hit the mark, just a bit rushed. Check out Cody’s blog for an opportunity to ingest it at a pace more appropriate for consumption with coffee or tea.

If you are making the transition from spinning or hybrid storage to all-flash, find the audio for this session and retrain your thinking. Offload old fears to VM-to-datastore limits and RAID considerations. Get simple. Be pure.

Live Notes & Commentary

Agenda

1. Trends in the DC architecture and intro to flash
2. Current integration & roadmap
3. Customer experience
4. Best practices & updates
5. Space reclamation
6. Q&A

Trends

CPU & Memory: Moore’s Law

Network:

• 10G adoption moving to 40G
• Low latency switches
• Policy driven networks
• SDN gaining ground

Storage: Flash storage

Virtualization & Storage in the Old World

• Legacy storage with spindle drives
• Capacity drives: more drives –> more IOPS
• Aggregates
• Performance tiers
• Short stroking disks
• Hot & cold disk data
• Tiers & caches
• Power, cooling, data center space — huge
• Best practices tuned to cater large disk arrays

Virtualization & Storage in the New World

• Storage based on all-flash or SSD drives
• Drives sizes ranging from 512GB to 4TB
• Massive amounts of IOPS with great latency & bandwidth
• Radically new approach to deal with flash media
• Data reduction techniques
  • Helps to reduce costs
  • Brings greater storage efficiencies
• Negates the need of performance tiers and caches
• Less power, cooling, and datacenter space
• iPhone level simplicity

Should it be any different in the new world?

• Easy:
  • No IOP calculation
  • No RAID decisions
  • No performance balancing
  • No workload isolation
  • No wasted space
• Performance increases 1000X
• Operational benefits 10X

Integration aspects

• vSphere plug-ins
• Scripting & cmdlets
• Large LUNs & datastores
• VAAI criticality

UC Davis Campus Data Center Customer Focus

Things to still consider with flash

• SCSI UNMAP
• Per VM IOPS limits — turn it off
• VMs that write larger than 64K chunk sizes
• VM saturating 10Gb network switch

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VMware VAAI: Unlocking Flash

• Atomic Test & Set (ATS) hardware-assisted locking
• Full Copy (XCOPY)
• Block Zero (WRITESAME)

XCOPY in vSphere 5.x

• Thin virtual disks grow in 1MB chunks–leads to fragmentation, not contiguous
• ESXi did not use the MaxHWTransferSize with thin disks–used VMFS block size of 1MB

XCOPY in vSphere 6.0 (enhancement)

• Now adheres to MaxHWTransferSize for thin virtual disks
• Attempts to maximize each command

Space Allocation & Virtual Disk Type

• Base capacity doesn’t make a difference with disk types

Virtual Disk Choice Revisited: Only Two Concerns Now

• Management ease (thin vs thick)
• Space reclamation

Space Reclamation (UNMAP): Why?

• With block storage–array does not control the file system
• Dead space is preserved on the array until…

…What?

• UNMAP: T10 SCSI operation
• Automates this reclamation process, built into Windows 2012 R2, Linux ext4

…Why Now?

• Least efficient: in a physical server world, less of a problem
  • deletions smaller
  • thin less common
• More efficient: in a virtualized world, more important
  • deleted files are entire virtual disks or VMs
  • thin is common throughout the stack
• Most efficient: imperative in all-flash array reduction arrays
  • reclamation helps regain efficiency of flash

History of UNMAP in vSphere

• ESXi 5.0 (mid-2011)
  • Automatic support introduced — overloaded or timed out arrays
• ESXi 5.0 P2 (end-2011)
  • Automatic UNMAP disabled
• ESXi 5.0 U1 (2012)
  • VMFS UNMAP in vmkfstools
• ESXi 5.5 (2013)
  • Added to esxcli
• ESXi 6.0 (2015)
  • In-guest UNMAP introduced

In-Guest Space Reclamation (UNMAP): How?

• Traditional in-guest space reclamation is tough
• UNMAP cannot traverse the many levels of SCSI virtualization
• Space had to be reclaimed by zeroing out empty space inside guest
  • sdelete, dd, etc
  • Array discards the zeroes
  • Space returned to free pool

vSphere 6: In-Guest UNMAP

• End-to-end UNMAP fully supported
• Zeroing not required for supported configurations
• Enable the option “EnableBlockDelete”
• Requires
  • ESXi 6.0
  • VM hardware version 11
  • EnableBlockDelete set to 1 (disabled by default)
  • Guest OS that can issue SCSI-2 UNMAP
  • Thin virtual disk

Virtual Volumes & UNMAP

• Space reclaimed automatically: No more VMFS UNMAP
• viols provide guest OS more direct SCSI control: in-guest UNMAP support, etc
• No more worrying about VMware configuration to provide UNMAP support

Expectations about UNMAP

• Running UNMAP doesn’t guarantee anything…
  • Physical capacity
  • Increase/decrease data reduction
• UNMAP is a housekeeping responsibility

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VMworld 2015 | Tuesday | Flash Storage Best Practices & Technology Preview (STO6326-SPO)

Cody Hosterman, Pure Storage | Ravi Venkat, Pure Storage