Last night I installed a 1 TB internal drive in my Macbook Pro to complement my SSD (I have no CD drive). 60% of the time, performance is great. The other 40%, it hangs severely and can't read or write anything for several seconds. Does anybody know what could be causing this? For reference, here's what disk usage looks like during a large copy operation (notice it flatlines at 0, even though the copy is still going): This drive is a Western Digital, but I had the same problem with a 1 TB Samsung a little while back. Samsung told me the drive was defective, but given I'm having the exact same behavior with a different drive, I'm thinking it's not a hardware issue after all. I formatted the drive with the Mac OS Extended (Journaled) file system. Running repair from disk utility finds no issues. I have tried disabling Apple's Sudden Motion Sensor and disabling Spotlight indexing on the drive. Neither makes a difference. Temporarily split it into two partitions to run a couple tests, but not planning to keep it that way. Here is what System Profiler reports: WDC WD10TPVT-00HT5T1: Capacity: 1 TB (1,000,204,886,016 bytes) Model: WDC WD10TPVT-00HT5T1 Revision: 01.01A01 Serial Number: WD-WXB1AB0T3611 Native Command Queuing: Yes Queue Depth: 32 Removable Media: No Detachable Drive: No BSD Name: disk1 Rotational Rate: 5200 Medium Type: Rotational Partition Map Type: GPT (GUID Partition Table) S.M.A.R.T. status: Verified Volumes: Capacity: 209.7 MB (209,715,200 bytes) Writable: Yes BSD Name: disk1s1 Media HD: Capacity: 386.61 GB (386,612,887,552 bytes) Available: 99.27 GB (99,267,100,672 bytes) Writable: Yes File System: Journaled HFS+ BSD Name: disk1s2 Mount Point: /Volumes/Media HD Media HD 2: Capacity: 613.11 GB (613,113,806,848 bytes) Available: 409.97 GB (409,971,826,688 bytes) Writable: Yes File System: Journaled HFS+ BSD Name: disk1s3 Mount Point: /Volumes/Media HD 2 Much appreciation in advance for any help.