22
votes
5answers
2k views

Why is iterating over a file twice faster than reading it into memory and computing twice?

I'm comparing the following tail -n 1000000 stdout.log | grep '"success": true' | wc -l tail -n 1000000 stdout.log | grep '"success": false' | wc -l with the following log=$(tail -n 1000000 ...
3
votes
3answers
164 views

Can I just disable updatedb?

Is updatedb necessary at all? I never use locate and my servers tend to have dozens of millions of files which usually makes updatedb to run for a long time and consume I/O needed by MySQL and/or ...
2
votes
2answers
253 views

Massive, unpredictable I/O performance drop in Linux

I'm using Debian testing without any problems for ~6 years (I'm just regularly updating it), but recently it started to show a random behaviour that can be summarized as "Low I/O performance which ...
4
votes
2answers
167 views

Why do systems become slow when doing massive writes to disk?

I want to know why systems become slow when writing mass data to disk. I think that for system to become slow, there should be some issue with CPU. But write is only I/O bound. Do hardware ...
1
vote
1answer
140 views

Does symlinking from Drive A to Drive B affect I/O on Drive A?

I was wondering if IO through a symbolic link affects IO on the host drive even if it points to a seperate drive? My setup is, /dev/sdb2 1.8T 443G 1.3T 26% /home1 /dev/sda3 1.8T 1.7T ...
5
votes
1answer
750 views

What keeps one side of an rsync so busy?

I've got a debian machine in my lan serving as a backup server for the others. It has four HDDs combined into a software RAID 5 md device, on that an lvm, and on that a btrfs. Backups are made using ...
2
votes
1answer
235 views

How do I record disk performance on slow hardware and then replay it to faster hardware and benchmark it?

I am currently performing various development tasks that are slow on my current system because of IO performance. Is there a way to record disk operations while performing IO consuming tasks, ...
2
votes
2answers
997 views

vmstat IO stats: why the high bo during a download?

On my RHEL 4 machine, I was downloading a huge file (2.5GB)..I was checking the output of vmstat and was especially curious about seeing the disk IO using bi and bo. I know iostat is a better tool ...
5
votes
1answer
771 views

SysBench highlighting abysmal disk write performance on white box vs Tier1 server

Have been testing white box system with SuperMicro X8DTL motherboard with various SATA hard disks such as 7,200RPM Seagate Constellation ES and 10,000 RPM Western Digital VelociRaptor. Have tested ...
4
votes
2answers
2k views

100.0%sy with poor disk performance

I have RHEL 5.4 kernel 2.6.18-164.el5 and I am experiencing very bad disk performance that happens randomly during working with Oracle. Nothing appears in the logs. When it happens, I see one CPU ...
2
votes
0answers
430 views

GNU/Linux, IO performance problems

I have some problems with my system performance. As I was adviced here, I used sar: $sar -u 5 and found out that the problems are caused by a low HDD performance, as I supposed (high %iowait). ...
1
vote
1answer
250 views

performance on Linux system when daisy-chaining multiple USB hard-drives on USB hubs?

What would the I/O access be like as I plug many USB drives into a Linux system with only 2 USB 2.0 ports and 1 USB 3.0 port? I expect I will have to have multiple levels of fan-out by plugging hubs ...
0
votes
1answer
133 views

What Linux tool will tell me if all the mounted disks share roughly the same bandwidth?

What Linux tool will tell me if all the mounted disks share roughly the same bandwidth? Can I do something like iostat for each of my /dev/sd* devices?
2
votes
1answer
295 views

Pluggin a bunch of USB hard drives into a Linux system?

I've got a Linux system with two USB 2.0 ports and one USB 3.0 port, and I would like to know how many USB hard drives I could plug into it. On the performance side, what would the I/O access be like ...
0
votes
1answer
268 views

How to test the difference between using disk encryption or not?

If I have a laptop, and I want to install an Ubuntu 11.04 on it, but disk performance would be an important thing, then how could I test the real differences between: - not using encryption - ...
4
votes
2answers
2k views

Hight iowait while the wMB/s is low

I was indexing a MySQL table. It makes a high load on that computer. It seems due to a high iowait. But it also shows that the wMB/s is only 2.87. Isn't even a common SATA HDD able to handle more ...
4
votes
4answers
363 views

performance monitoring

Is there some performace monitoring tool which would run in background gathering info about all system activity? Somethimes my system (Arch linux, 32 bit) slows down terribly and the top utility ...
4
votes
1answer
521 views

“Split I/O”s on a Linux VM, disk alignment

I'm trying to figure out if there's some way I can tell if a system is being adversely affected by disk misalignment -- i.e. when I do a disk I/O operation, it actually needs to request extra blocks ...
13
votes
2answers
4k views

Why does high disk I/O reduce system responsiveness/performance?

I never quite understood why high disk I/O slowed the system so much. It's strange to me because I would expect the slow-down to affect only those processes dependent on the hard/optical drive data, ...
9
votes
1answer
1k views

What's the progress regarding improving system performance/responsiveness during high disk I/O?

Whenever there is high disk I/O, the system tends to be much slower and less responsive than usual. What's the progress on Linux kernel regarding this? Is this problem actively being worked on?
14
votes
2answers
2k views

Measure pipe throughput in the shell

There is a shell command that allows to measure how fast the data goes through it, so you can measure the speed of output of commands in a pipe. So instead of: $ somecommand | anothercommand you ...
8
votes
2answers
1k views

Heavy write activity on SSD nukes system performance

I've noticed that when I do heavy write applications, the whole system slows down. To test this further I ran this to do a (relatively) low-CPU, high disk activity: john -incremental > file_on_SSD ...
11
votes
1answer
521 views

How do I go about tracking down IO usage in Linux and other *nix OS'?

Occasionally, something on my system starts hammering the disk. I would like to log data that would let me know about I/O usage per process, then I could go back to it later and see what keeps doing ...
25
votes
12answers
2k views

How can I tweak my Linux desktop to be more responsive?

I have the experience that Linux works fine until the physical memory is exhausted. As soon as swap space is used the performance is severely degraded and the GUI becomes unresponsive. This problem ...