[SOLVED] SLOW DISK: 100MB/s read but only 2MB/s write!
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DISK:
WDC WD1003FBYX-0
CONTROLLER:
Intel 8 Series/C220 Series Chipset Family 4-port SATA Controller 1 [IDE mode]
Code:
# hdparm -tT /dev/sda
/dev/sda:
Timing cached reads: 22962 MB in 1.99 seconds = 11514.06 MB/sec
Timing buffered disk reads: 242 MB in 3.01 seconds = 80.49 MB/sec
Code:
# iotop WHILE READING: (copy big file from disk to ramfs)
Total DISK READ : 99.82 M/s | Total DISK WRITE : 2.27 M/s
Actual DISK READ: 99.82 M/s | Actual DISK WRITE: 1744.35 K/s
Code:
# iotop WHILE WRITING: (copy big file from ramfs to disk)
Total DISK READ : 711.29 K/s | Total DISK WRITE : 3.03 M/s
Actual DISK READ: 711.29 K/s | Actual DISK WRITE: 2.47 M/s
Drive can present incorrect physical sector size and I'm pretty sure it is the case here.
I looked up that model number on the WD website, and the specs there say the sector size is 512 bytes. Actually, the swap partition is properly aligned, so it should be possible to do some experimenting based on that (and the test I proposed above might not be meaningful).
And now that I notice the results in #9, I can only conclude that something seems seriously wrong with that drive. That test was doing I/O to a properly aligned partition. Let's see the output from "smartctl -A /dev/sda" and see if that reveals anything.
Last edited by rknichols; 05-26-2014 at 04:56 PM.
Reason: And now that I notice ...
System uptime is irrelevant. The drive accumulates those events internally whenever it is on.
Well, I'm at a loss to explain what is happening. Those SMART attributes all look excellent -- no bad sectors, nothing out of the ordinary. Unless some other process is pounding on the disk or /var/log/messages is overflowing with ATA error messages, I can't imagine what could be going on. Even if there were an alignment issue (which has been ruled out anyway), a 50:1 degradation would be beyond anything I've heard about. This is an ordinary internal disk, not part of some network storage or RAID array, right? By any chance is the BIOS set up for RAID, and writes are always waiting for a missing disk in the array?
Or, perhaps everything you write to the disk is first being sent to the NSA for inspection/audit??
Alright. I'm trying one more time. IDE mode is compatibility mode for Windows XP users so they can boot and install AHCI drivers. Quite clear it is not designed for performance ... ?
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