Improving Disk Latency and Throughput with VMware Presented by Raxco Software, Inc. March 11, 2011

Today’s Agenda Provide technical information on how NTFS impacts VMware I/O performance Examine ESX I/O test results Economic impact of Windows guests Solutions

Virtualization Benefits Server consolidation Less physical space for data centers Lower energy costs Easier management Eco-friendly alternative

Identifying and Correcting Problems Latency is your best indicator of a performance problem –Device latency is vSphere’s report of the physical storage response time –Kernel latency is vSphere’s report of ESC’s ability to manage IO Experts disagree on specifics, but most agree that… Device latency in excess of 15ms is worth inspection Device latency in excess of 30ms is likely a problem Kernel latency in excess of 2ms means ESX queues are overflowing High device latency can result in ESX queuing –So, correct slow hardware first! –Then, consider reducing VMDKs on a VMFS volume –Only then consider changing queue depths © Copyright 2010 EMC Corporation. All rights reserved.

Storage Contention Solution: Storage IO Control SIOC calculates data store latency to identify storage contention –Latency is a normalized, average across virtual machines –IO size and IOPS included SIOC enforces fairness when data store latency crosses threshold –Default of 30ms –Fairness enforced by limiting VMs access to queue slots Net effect: trade throughput for latency © Copyright 2010 EMC Corporation. All rights reserved. With Storage IO Control Actual Disk Resources utilized by each VM are in the correct ratio even across ESX Hosts

NTFS I/O Storms

NTFS Behavior NTFS fragments files and free space Increases logical I/O to storage controller More logical I/O = More physical I/O Multiple instances of Windows on host can lead to I/O contention

What is Fragmentation? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

Logical v Physical Logical Level – NTFS needs disk and cluster size, enumerates LCNs – Creates $MFT and $Bitmap metadata – $Bitmap is how NTFS “sees” the disk – Has no idea about physical/virtual disk types

Anatomy of an MFT Record (vcn, lcn, run length): (8a85, 9189a, 7)

File Allocation Create $MFT record (one or more) $Bitmap accessed to locate free space $MFT record is updated with content Create Bitmap Access MFT Update

File Access Load portion of MFT with correct record via directory Locate file in the MFT Pass starting LCN’s and run lengths to disk controller Number of logical fragments influences number of physical seeks Load Locate File # LCN’s # Physical Seeks

Logical v. Physical Physical Level – Disk controller Maps LCNs to PCNs – Writes data to disk

Wasted Seeks Partition State Total Number of I/O Requests Sent to the File System Total Number of Resulting Disk Accesses/Seeks Net Wasted Seeks When Running SYSmark Percent Net Wasted Seeks When Running SYSmark Fragmented 1,320,6862,090,649769, % After PerfectDisk 1,434,4541,616,847182, % After Built-In1,411,6131,931,395519, %

How This Affects A Virtual Environment P2V Conversion Extra Hypervisor Overhead Disk Latency Degradation Overall Performance System Throughput Wasted Space Costly

P2V Conversion Physical Drive No Optimization Optimization 24GB 22GB 2GB Smaller

ESX Cluster Testing Identical disks - 40% free space Optimized one set, the other “as is” Installed MS Office and MS SQL Captured metrics with VMware’s vscsiStats utility

Fragmented PerfectDisk % Improvement Total IO Count Read IO Count Write IO Count Total I/O Count

30ms50ms100ms>100ms Total Fragmented I/O ,442 PerfectDisk I/O ,764 49% Reduction in Latency!

Disk Latency

Fragmented DiskPerfectDisk Disk Total IO Equal to 524K Total IO > 524K Read IO Equal to 524K 337 Read IO >524K12565 Write IO Equal to 524K Write IO >524K X More Large I/O

12 times more of the largest IO Large I/O

Improved Sequential I/O FragmentedPerfectDiskImprovement Percent Sequential17%27% 58% Total IO % Sequential IO %

Improved Sequential I/O

Installation Time Comparison FragmentedPerfectDisk% Improvement MS Office Install20 min15 min 25 MS SQL Install76 min51 min 33

The Cost of Fragmentation EXAMPLE: 20 files x 6 seconds = 2 minutes 300 users x 2 min = 10 hours/day 10 hrs x $25/hr = $250/day Annual cost = $62,500

Virtual Guest Fragmentation Windows guests have all the same NTFS behavior Fragmentation produces more IOPS Fragmentation reduces ESX throughput Fragmentation increases ESX disk latency Fragmentation creates resource contention between host & guests

Solutions Expensive – More disks and faster disks – Upgrade Fibre Channel – Troubleshooting Inexpensive – Optimize the Windows guest systems

PerfectDisk 12 vSphere Virtualization Awareness/host & client OptiWrite Fragmentation Avoidance “Zero-fill” free space NEW

PerfectDisk 12 vSphere “Short stroking” for thin provisioned disks Schedule guest compaction Snapshot & Linked Clone recognition NEW

PerfectDisk Benefits on ESX Saves $$$ in productivity and admin Reduces resource contention for VM’s Reduces total IO workload Improves throughput Reduces disk latency Delivers optimal performance

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