27 inch iMac suddenly running very slowly

iMac (27-inch, Mid 2011) (Verified)

iMac - model: iMac12,2

1 3.1 GHz Intel Core i5 CPU: 4-core

4 GB RAM Upgradeable

OSX 10.10 (Yosemite)

My Mac suddenly slowed down on Monday or Tuesday of last week. Response time from mouse click to system response is sometimes in the 10s of seconds. This was not a gradual slow down. It happened quite suddenly.

I've run Disk Utility from recovery boot -- fixed permissions and verified disk. Disk showed no issues but I clicked repair anyway. Ran Apple Hardware Test; it says no hardware issues. No change.

Here's what etrecheck shows:

Problem description:

Very slow system response. Often tens of seconds between mouse click and system action.

EtreCheck version: 2.0.11 (98)

Report generated November 8, 2014 at 10:40:28 PM EST

Hardware Information: ℹ️

iMac (27-inch, Mid 2011) (Verified)

iMac - model: iMac12,2

1 3.1 GHz Intel Core i5 CPU: 4-core

4 GB RAM Upgradeable

BANK 0/DIMM0

2 GB DDR3 1333 MHz ok

BANK 1/DIMM0

2 GB DDR3 1333 MHz ok

BANK 0/DIMM1

empty empty empty empty

BANK 1/DIMM1

empty empty empty empty

Bluetooth: Old - Handoff/Airdrop2 not supported

Wireless: en1: 802.11 a/b/g/n

Video Information: ℹ️

AMD Radeon HD 6970M - VRAM: 1024 MB

iMac 2560 x 1440

System Software: ℹ️

OS X 10.10 (14A389) - Uptime: 2:34:50

Disk Information: ℹ️

ST31000528AS disk0 : (1 TB)

S.M.A.R.T. Status: Verified

EFI (disk0s1) <not mounted> : 210 MB

iMac HD (disk0s2) / [Startup]: 999.35 GB (617.61 GB free)

Recovery HD (disk0s3) <not mounted> [Recovery]: 650 MB

OPTIARC DVD RW AD-5690H

USB Information: ℹ️

Apple Inc. FaceTime HD Camera (Built-in)

Apple, Inc. Keyboard Hub

Apple Inc. Apple Keyboard

Apple Inc. BRCM2046 Hub

Apple Inc. Bluetooth USB Host Controller

Logitech USB-PS/2 Optical Mouse

Apple Internal Memory Card Reader

Apple Computer, Inc. IR Receiver

Thunderbolt Information: ℹ️

Apple Inc. thunderbolt_bus

Gatekeeper: ℹ️

Mac App Store and identified developers

Launch Agents: ℹ️

[loaded] com.oracle.java.Java-Updater.plist Support

[running] com.rosettastone.rosettastonedaemon.plist Support

Launch Daemons: ℹ️

[loaded] com.adobe.fpsaud.plist Support

[loaded] com.oracle.java.Helper-Tool.plist Support

[loaded] com.oracle.java.JavaUpdateHelper.plist Support

User Launch Agents: ℹ️

[loaded] com.adobe.ARM.[...].plist Support

[invalid?] com.citrixonline.GoToMeeting.G2MUpdate.plist Support

[loaded] com.facebook.videochat.[redacted].plist Support

[loaded] com.genieo.completer.download.plist Support

[loaded] com.genieo.completer.ltvbit.plist Support

[loaded] com.genieo.completer.update.plist Support

[loaded] com.google.keystone.agent.plist Support

[loaded] com.valvesoftware.steamclean.plist Support

[running] net.optimum.iptv.optimumapp.agent.v3.plist Support

[running] opt.plist Support

User Login Items: ℹ️

iTunesHelper UNKNOWN (missing value)

Quicken Scheduler application (/Applications/Quicken 2007/Quicken 2007/Contents/SupportApps/Quicken Scheduler)

OpenDNS Updater Application (/Applications/OpenDNS Updater.app)

Music Manager UNKNOWN (missing value)

Android File Transfer Agent Application (/Users/[redacted]/Library/Application Support/Google/Android File Transfer/Android File Transfer Agent.app)

Google Drive Application (/Applications/Google Drive.app)

Dropbox Application (/Applications/Dropbox.app)

Google Chrome Application (/Applications/Google Chrome.app)

Music Manager Application (/Users/[redacted]/Library/PreferencePanes/MusicManager.prefPane/Contents/Helpe rs/MusicManagerHelper.app)

iTunesHelper UNKNOWN (missing value)

HP Scheduler Application (/Library/Application Support/Hewlett-Packard/Software Update/HP Scheduler.app)

Internet Plug-ins: ℹ️

Flip4Mac WMV Plugin: Version: 3.0.0.85 BETA - SDK 10.7 Support

FlashPlayer-10.6: Version: 15.0.0.152 - SDK 10.6 Support

Default Browser: Version: 600 - SDK 10.10

AdobePDFViewerNPAPI: Version: 11.0.09 - SDK 10.6 Support

AdobePDFViewer: Version: 11.0.09 - SDK 10.6 Support

Flash Player: Version: 15.0.0.152 - SDK 10.6 Mismatch! Adobe recommends 15.0.0.189

QuickTime Plugin: Version: 7.7.3

OfficeLiveBrowserPlugin: Version: 12.3.6 Support

Unity Web Player: Version: UnityPlayer version 4.5.0f6 - SDK 10.6 Support

Silverlight: Version: 5.1.30514.0 - SDK 10.6 Support

JavaAppletPlugin: Version: Java 8 Update 25 Check version

User Internet Plug-ins: ℹ️

CitrixOnlineWebDeploymentPlugin: Version: 1.0.105 Support

Safari Extensions: ℹ️

Omnibar

Audio Plug-ins: ℹ️

DVCPROHDAudio: Version: 1.0

3rd Party Preference Panes: ℹ️

Flash Player Support

Flip4Mac WMV Support

Java Support

MusicManager Support

Time Machine: ℹ️

Skip System Files: NO

Auto backup: YES

Volumes being backed up:

iMac HD: Disk size: 999.35 GB Disk used: 381.73 GB

Destinations:

500 GB External [Local]

Total size: 499.45 GB

Total number of backups: 36

Oldest backup: 2014-10-26 22:03:51 +0000

Last backup: 2014-11-08 13:22:06 +0000

Size of backup disk: Too small

Backup size 499.45 GB < (Disk used 381.73 GB X 3)

Top Processes by CPU: ℹ️

4% WindowServer

2% MusicManagerHelper

1% systemstatsd

1% AppleSpell

0% Google Chrome

Top Processes by Memory: ℹ️

125 MB Dock

116 MB Finder

90 MB mds_stores

82 MB Google Chrome

77 MB mds

Virtual Memory Information: ℹ️

195 MB Free RAM

1.62 GB Active RAM

1.43 GB Inactive RAM

805 MB Wired RAM

3.42 GB Page-ins

193 MB Page-outs

Saw on another thread the suggestion to run Console and see what the logs were saying. Here's a sample -- looks pretty ominous:

11/8/14 11:57:52.210 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles) Service only ran for 0 seconds. Pushing respawn out by 10 seconds.

11/8/14 11:58:02.252 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles[3936]) Could not find uid associated with service: 0: Undefined error: 0 1422

11/8/14 11:58:02.253 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles) Service only ran for 0 seconds. Pushing respawn out by 10 seconds.

11/8/14 11:58:02.932 PM system_profiler[3935]: platformPluginDictionary: Can't get X86PlatformPlugin, return value 0

11/8/14 11:58:02.933 PM system_profiler[3935]: platformPluginDictionary: Can't get X86PlatformPlugin, return value 0

11/8/14 11:58:03.000 PM kernel[0]: 13893.822791: apple80211Request[10514] Unsupported ioctl 181

11/8/14 11:58:12.261 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles[3954]) Could not find uid associated with service: 0: Undefined error: 0 1422

11/8/14 11:58:12.261 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles) Service only ran for 0 seconds. Pushing respawn out by 10 seconds.

11/8/14 11:58:22.280 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles[3955]) Could not find uid associated with service: 0: Undefined error: 0 1422

11/8/14 11:58:22.281 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles) Service only ran for 0 seconds. Pushing respawn out by 10 seconds.

11/8/14 11:58:32.288 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles[3956]) Could not find uid associated with service: 0: Undefined error: 0 1422

11/8/14 11:58:32.288 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles) Service only ran for 0 seconds. Pushing respawn out by 10 seconds.

11/8/14 11:58:42.303 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles[3957]) Could not find uid associated with service: 0: Undefined error: 0 1422

11/8/14 11:58:42.303 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles) Service only ran for 0 seconds. Pushing respawn out by 10 seconds.

11/8/14 11:58:52.312 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles[3958]) Could not find uid associated with service: 0: Undefined error: 0 1422

11/8/14 11:58:52.313 PM com.apple.xpc.launchd[1]: (com.apple.mdworker.bundles) Service only ran for 0 seconds. Pushing respawn out by 10 seconds.

11/8/14 11:58:55.000 PM kernel[0]: disk0s2: I/O error.

11/8/14 11:58:55.049 PM systemstatsd[346]: assertion failed: 14A389: systemstatsd + 3269 [8BF02DBC-09E8-3994-8C2D-1C0A869EF157]: 0xa

11/8/14 11:58:55.471 PM Google Chrome[277]: Error launching spell checker for Multilingual: Error Domain=NSCocoaErrorDomain Code=256 "The application “AppleSpell” could not be launched because a miscellaneous error occurred (OSStatus -1712)." UserInfo=0x7d40fa70 {NSURL=file://localhost/System/Library/Services/AppleSpell.service, NSUnderlyingError=0x7d40f9c0 "The operation couldn’t be completed. (OSStatus error -1712.)", NSLocalizedDescription=The application “AppleSpell” could not be launched because a miscellaneous error occurred (OSStatus -1712).}

11/8/14 11:58:56.040 PM AppleSpell[313]: *** -[NSMachPort handlePortMessage:]: dropping incoming DO message because the connection is invalid

It's not showing as much in the excerpt above, but I'm getting lots of those "kernel: disk0s2: I/O error" messages. Sounds like HD failing? Why would Disk Utility say everything is fine?

Any help would be appreciated!