@Trevor scenary from the sysadmin's production war room !!
common arsenal we generally have at our end are :
iostat
iotop
dstat
sar
lvmstat ( for AIX )
focus on these 2 parameters in the output :
await: Average time for I/O requests to be fully serviced from queue to completion.
%util: Device’s busy time percentage : shows how loaded your disk (or LVM layer) is.
1. iostat -d -z 2 or iostat -d -p sda
If both your physical disk and the logical volume (LV) are showing high utilization and long wait times, it means you've likely hit the performance limits of the physical disk itself. Think of it like a single-lane road that's completely backed up with too many cars.
If your LV is slow and has a lot of waiting requests, but the physical disk itself is relatively idle, the problem is most likely in the LVM layer. This can happen because of a poor setup, like a bad way of distributing data (suboptimal striping) or copying it (mirroring). The road is fine, but the traffic management system on it is what's causing the slowdown.
2. iotop - if your Linux server suddenly slows down, the iotop command in Linux can help you determine which processes are overloading the disk. Identify whether a single process is choking the LV, leading to higher load and misleading utilization patterns at the LVM level.
3. dstat -cdl -D sda - compare physical vs logical throughput. key indicators to check are : Utilization and transactions per second (--disk-util, --disk-tps).
4. sar -d 1 5 or sar -d -b to capture I/O metrics over intervals. If you compare the performance history of your physical disk to its Logical Volume, you might find a mismatch. If the Logical Volume shows consistent spikes in activity, but the physical disk I/O stays stable, that is a sign to start looking into LVMs internal behavior. It means the issue isn ot with the hardware; it's with how LVM is managing the data.
Sometimes you see a lot of small, quick I/O operations with low total throughput. This usually happens with things like database work or log writing. To fix this, you might need to use an SSD to get faster operations per second (IOPS), add a caching layer, or just optimize your queries.
On the other hand, if you see a small number of operations but the throughput is very high, it means you're moving a few really big files. This is common during file transfers, backups, or media processing. If you're having trouble with speed here, consider using RAID or NVMe drives for better sustained performance.
https://man7.org/linux/man-pages/man1/iostat.1.html
https://linux.die.net/man/1/iotop
https://man7.org/linux/man-pages/man1/sar.1.html
https://linux.die.net/man/1/dstat
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