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Questions tagged [io]

IO (or I/O) is an abbreviation for input/output, most commonly referring to disk input/output.

IO (or I/O) is an abbreviation for input/output, most commonly referring to disk input/output.

401 questions
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What creates CPU I/O wait but no disk operations?

I have CPU I/O wait steady around 50%, but when I run iostat 1 it shows little to no disk activity. What causes wait without iops? NOTE: There no NFS or FUSE filesystems here, but it is using Xen virtualization.
Jason Cohen
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How does Linux handle concurrent disk IO?

When a Linux server is serving many concurrent requests to read many different files, does it: Seek to File_1, read the entire file, then seek to File_2, read the entire file, then seek to File_3, etc etc Seek to File_1, read part of it (up to the…
Continuation
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how to do I/O sniffing

For sizing purposes I need to understand what requirements an application has to the I/O subsystem. I would love to do what I call I/O sniffing and obtain a list of events from the block layer like this: initiator XYZ requests block 4711 from device…
Thorsten Staerk
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linux: how to simulate hard disk latency? I want to increase iowait value without using a cpu power

Is it possible to set an arbitrary delay for I/O operations? I would like to learn how do iowait and disk %util impact the performance. There are a lot of tools to stress the disk (bonnie++ etc.) but I'm looking for a way to introduce a delay like…
user156233
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How do you monitor the performance of a character device (e.g. tape drive)?

There are many ways to monitor block device performance: dstat and iostat, heck, even sar will give you data on block device I/O rates. Unfortunately, I don't know of any good spur-of-the-moment tools for monitoring the performance of a character…
Slartibartfast
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How to identify heavy write to disk?

I have this problem with server running CakePHP application. The server is insanely slow, I first thought that it's application problem, but then I found constant 5-6MB/s write to disk. What is the easiest way to find cause of such a heavy…
Jakub Arnold
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MySQL extremely slow on very simple SELECT queries

We have a simple web application running on a virtual machine that saves its data in a MySQL 5.5 database with the InnoDB engine. Everything worked fine for around three years, but suddenly it became extremely slow. For example, I have a very simple…
tabb
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What does it mean when Linux has no I/O scheduler

I have some virtual machines running Ubuntu cloud-based image 14.04-1 LTS version. I wanted to see the IO performance of different IO schedulers on the VM so I went to /sys/block//queue/scheduler on the guest OS to change the IO scheduler.…
Ha Son Hai
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Is there a way to delete 100GB file on Linux without thrashing IO / load?

I have a huge log file I need to delete on a production web server. I'm worried it'll bring the system to a crawl if I rm it on Linux. Any brilliant ideas? Update: Filesystem: ext3 Partition: /var (mostly logs and MySQL data) Log file is no longer…
objectoriented
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Interpreting read, write and total IO time in /proc/diskstats

I've noticed that when I look at the output of /proc/diskstats there is a discrepancy between the total time spent reading, the total time spent writing, and the total time performing IO. For example, I saw an entry in /proc/diskstats that was: $…
jeromefroe
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Why do sequential writes have better performance than random writes on SSDs?

An LBA (logical block addresses) is a mapping table implemented in the FTL to match between logical and physical pages/blocks in SSDs, my guess is that most SSDs (at least when they are empty) keeps the physical addresses in the same order as the…
SamTh3D3v
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High load due to I/O wait in Ubuntu 12.04 on EC2 instance

I am using Ubuntu server 12.04 , having trouble finding cause of load, I have seen change in response time of server from past week after reading Linux Troubleshooting, Part I: High Load It seems like there is no issue with CPU and RAM, and this…
Straw Hat
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Windows "iowait" CPU utilization reporting

Does Windows account for and report "iowait" in the same manner as Linux? That is, processes enter "uninterruptible sleep" and their time spent is subtracted from "CPU free"? If so, which Perfmon counters would be appropriate to detect "cpu busy due…
Yolo Perdiem
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Amazon RDS: What are IO Requests?

I have an RDS instance that is costing me a lot of money. From my account activity on amazon I see that the instance has had about 800,000,000 IO requests over the past 7 days. To give you a little perspective, my app only gets about 6,000 unique…
Abe
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Logging hurts MySQL performance - but, why?

I'm quite surprised that I can't see an answer to this anywhere on the site already, nor in the MySQL documentation (section 5.2 seems to have logging otherwise well covered!) If I enable binlogs, I see a small performance hit (subjectively), which…
James Green
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