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Questions tagged [io]

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

2
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2answers
25 views

Which process writes/reads the most from disk over time? [on hold]

I want to know which process writes/reads the most from disk over time, I mean that I will start the monitoring process than after X time I will be able to see what was the process that used the disk ...
0
votes
0answers
52 views

What could cause Nginx to write this much I/O?

I have a high-traffic webserver (up to ~50 page loads per second) running nginx, which passes HTML requests to a PHP-FPM backend and serves static assets directly. Under this load, I get a curiously ...
0
votes
0answers
60 views

Disk access too slow in ubuntu virtual server

I have an ubuntu 18.04 virtual server, and I believe there is something wrong with the disk access. opening normal small files takes a long time and websites frequently time out without any specific ...
0
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0answers
14 views

Tool to generate IOWaits

In order to test our monitoring infrastructure, I'd like to generate enough IOs to trigger an alert. As the alert is based on IOWaits, I should find a way to 'overload' the IOs. I found an article ...
0
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0answers
29 views

I/O performance issues with dd “benchmark” on XenServer 7.1 using SLES12-SP3 in HVPVM mode

Why does SLES12-SP3 in HVPVM mode perform that badly compared to the other two? SLES12-SP3 VM inside ESXi 5.5: Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz ...
1
vote
2answers
582 views

What does iodepth in fio tests really mean? Is it the queue depth?

I understand queue depth which is the number of outstanding I/O requests that the storage controller can handle (https://www.tomshardware.com/reviews/ssd-gaming-performance,2991-3.html) i.e., this is ...
3
votes
3answers
47 views

Are there any industry standards for network timeout or / IO timeout etc? [closed]

I was reading this article about microbursts: https://www.cisco.com/c/en/us/products/collateral/switches/nexus-5000-series-switches/white-paper-c11-733020.html which can also cause traffic drops. ...
5
votes
2answers
1k views

what is the relation between block size and IO?

I have been reading about disk recently which led me to 3 different doubts. And I am not able to link them together. Three different terms I am confused with are block size, IO and Performance. I ...
0
votes
0answers
22 views

Give read operations priority over write

I'm working on a system where I have a program that outputs high quality videos for a tv connected to an HDMI (raw 1080p data for instance) and I'm having an issue that when I copy some files to my ...
0
votes
1answer
476 views

Backup with rsync painfully slow

I'm using rsync to perform backups from an NFS server hosted in AWS to another EC2 instance in the same AZ, the rsync command that I'm using in the backup server is the following: rsync -avzb --...
0
votes
0answers
196 views

Strange await times in iostat output

I am seeing strange big numbers as w_await times (like 5 million ms) on a server with 2x SSD in MD RAID1. Scheduler is deadline. OS is Debian 9 with kernel 4.9.65-3+deb9u1. Is this just some sort of ...
0
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2answers
112 views

Should sector-unaligned HDD writes be slower than sector-aligned writes?

Background: I'm planning to use ZFS and I need to find the correct ashift parameter for my harddrive, which should be log2(sector_size), e.g. 9 for 512 byte sectors. My harddrive reports a physical ...
0
votes
1answer
146 views

Linux: how can I determine if an application is doing sequential or random disk I/O?

Everyone knows that databases tend to do lots of small random I/O while big data things like Kafka tend to do large sequential I/O, but if I'm approaching this as a sysadmin without making assumptions,...
2
votes
2answers
578 views

Mariadb 10.3 high disk write rates

With the help of some other fine people here, I have found the high loads we have been experiencing lately are related to mysqld high disk write rate seen in iotop. With a load average now 3-6 where ...
0
votes
1answer
182 views

What are the parameters in iostat

I used iostat and trying to understand the iostat output using this link : https://linoxide.com/linux-command/linux-iostat-command/ but It is not clearly explained. PF the output at different times ...
2
votes
1answer
215 views

contradictory results dd and iostat, ext4 and xfs, on EBS volumes

I'm seeing what seems to me to be contradictory results when looking at disk performance with dd versus iostat on two hosts (EC2 instances with an EBS drive). The hosts are identical except that one ...
1
vote
1answer
74 views

How can I prevent high-volume filesystem writes from ovewhelming memory on my Linux system?

In several contexts, I've seen a behavior on Linux systems in which large volumes of filesystem write operations (e.g., many gigabytes of writes, very quickly) will overwhelm memory, apparently ...
0
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0answers
28 views

Does Linux offer any way to force-unmount or disable a file system or block device on I/O error?

I've just learned that ext4's errors=remount-ro doesn't remount the file system read-only on errors. It remounts on file system metadata errors. So it cannot be trusted to take the FS offline if there'...
0
votes
1answer
43 views

Disk/Controller Performance Comparison

Since 2012 Iam using the HP Proliant Dl385 G7 with Smart Array P410i. 2xAMD Opteron 2.4GHz, 24 Cores System Disk C: 2xSAS 15k in RAID1 Some time ago I purchased a new HP Proliant Dl380 G9 with Smart ...
3
votes
1answer
155 views

Misunderstanding about Page Cache and dirty_background_bytes

I've been looking at this for a while now and things aren't lining up with my expectations, but I don't know if it's because something is off, or if my expectations are wrong. So, I've got a system ...
1
vote
1answer
347 views

file system corrupt in a virtual machine

I have a virtual machine hosted by vmware esxi. It has been started for over 80 days. And about ten days ago, its file system got corrupted. Although I can use fsck to fix this file system, I am ...
1
vote
1answer
299 views

Does ionice has any effect on NFS client?

I need to remove millions of directories recursively on a NFS share and to avoid any performance issues, I ran the command with: ionice -c 3 -t find /dir -type f -exec rm {}; which will delete all ...
-1
votes
1answer
2k views

VMWare - VM won't start - 5 (Input/output error) - failed drive

Basics: Server with 4 drives, 2 solid state. One of the solid state drives appears to have failed. Running VMWare 5.0 We tried to distribute the VMs over several disks and using RAID, but I'm not ...
1
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0answers
638 views

Troubleshooting `Buffer I/O error` on software-raid/md-device

I've got a RAID-5 mdadm array that reliably causes Buffer I/O error on dev md0, logical block 1598030208, async page read to be written do dmesg when reading that block. Of course, the read also ...
0
votes
2answers
70 views

How to determine if I/O is slow for server

I have used I/O stat to check whether my server's I/O is slow or not. The % util is high but so is the read/sec - write/sec. Can anyone help ? Following is the output of iostat -mx command Linux 2.6....
1
vote
1answer
591 views

How to check why a write failed? [closed]

If I was to debug a service on a machine and I determined that a write was failing, how could I check why the write failed? I know the system call in C will return -1 and then we can check what ...
0
votes
0answers
87 views

IO Latency - Cause or symptom?

Our application (LAMP) worked perfectly at our current VPS provider. Since few weaks ago we are experiencing very high load peaks (80+). We discovered that the CPU and memory are both normal during ...
6
votes
1answer
166 views

RAID6 resync with fast writes but slow reads

I'm using Debian Jessie. # uname -a Linux host 4.9.0-0.bpo.3-amd64 #1 SMP Debian 4.9.30-2+deb9u5~bpo8+1 (2017-09-28) x86_64 GNU/Linux And have setup a RAID6. # cat /proc/mdstat Personalities : [...
1
vote
1answer
687 views

Google compute: Why persistent ssd disks are slower than persistent standard disks?

I ran several IO benchmarks and I cannot understand how pd-ssd offers a worse IO throughtput than pd-standard. In my tests I boot a VM with a bootable disk pd-ssd of 30 or 250GB, and I still get ...
2
votes
0answers
1k views

KVM/QUEMU guest slow disk performance

I'm really confused of QEMU/KVM behavior. I have a server - about 100GB RAM, 2 CPU - 6 core + HT, and three HDDs - one for root, and two for BTRFS-mirror for virtual machines (HGST HDN724030ALE640 if ...
0
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0answers
264 views

Systemd process reads a lot from server hard drive

I noticed strange thing on one of my servers (Cloudlinux 7). The server has very few users and low traffic. Databases are on SSD drives. The server has more iowait than the other servers (with the ...
0
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0answers
97 views

Poor disk IO on Redhat VM on Hyper-V 2012 R2

We recently migrated a RedHat 5.11 virtual machine from an alternative provider (VMWare) to ourselves (HyperV). The machine boots and is online etc, but the IO sucks compared to pre-migration... ...
0
votes
1answer
169 views

How to determine a QEMU virtual machine is idle?

I am working on a KVM-QEMU virtual machine.Currently I want to find out whether a program (e.g., MySql) running inside the virtual machine is idle (i.e., not busy processing requests). I want to get ...
0
votes
1answer
24 views

Could the amount of files in a windows directory impact the time it takes to copy new files into it?

I have a export process that dumps new files into a folder on my Windows 7 PC each day (about 1-2K). This directory is now unusably slow to navigate through Windows Explorer with millions of files in ...
4
votes
1answer
10k views

Centos7 - Buffer I/O error on dev sda, logical block xxxxxxxxx, lost async page write

I have a webserver that have the content in HP MSA2040 Storage (10 tb total storage). I keep getting error like below Jul 31 19:06:24 xxxxxxxx*** kernel: blk_update_request: I/O error, dev sda, ...
2
votes
1answer
572 views

What does the nomerge mean in Linux system?

We can see some parameters by issuing "iostat -x -d", the rrqm/s and wrqm/s stand for the merge for I/O request per second. And there is a kernel parameter controlling the I/O merge: /sys/class/block/...
4
votes
1answer
2k views

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, ...
4
votes
0answers
50 views

Do I need to create multiple filesystems on a virtual server to increase I/O performance?

I want to install Oracle on a virtual server. I don't really know the technology behind, my company just gave me a virtual server with multiple (virtual) disks. I have the possibility to divide those ...
1
vote
2answers
32 views

A lot more write then read IO [closed]

As shown in the picture above we are having a lot more writes then reads on our appserver. Cache is enabled and the Framework is running with PHP/Symofony and using HTTP Cache. Is this I/O behavior ...
3
votes
1answer
613 views

Why is io scheduler not merging requests?

After some time (or amount of data written) after server reboot the write speed drops to less than 1 MB/s. This is regardless of which filesystem (also raw partition) and regardless of HDD (HW RAID) ...
0
votes
1answer
274 views

Does having a good or bad filesystem inside a Virtual machine really matters?

I want to understand how the IO is sent to hard disk blocks from a virtual machine. Does having a XFS or ext3 or ext4 etc. really matters inside a virtual machine, or it is just depended on the file ...
4
votes
2answers
2k views

Why does sequential writes have better performance than random writes in 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 ...
1
vote
0answers
94 views

AWS EC2 snapshot reaches IOPS limit occasionally

For an EC2 server I have running I am creating a snapshot of the EBS every night. The EBS has 500GB of space and 1500 / 3000 IOPS. On some days past week the snapshot creating process reached it ...
0
votes
2answers
170 views

e2fsck takes lot of time to run

I am running e2fsck on one of my disk partitions (ext4) but it seems to take eternity. It is already running now for almost 10 hours or so and it is still at 42%. The size of the partition is around ...
2
votes
1answer
442 views

Linux software RAID becomes unresponsive after removing a disk from server

I am running a CentOS 7 machine (standard kernel: 3.10.0-327.36.3.el7.x86_64) with a software RAID-10 over 16x 1 TB SSDs (to be more precise, there are two RAID arrays on the disks; one of the arrays ...
0
votes
1answer
103 views

Use deadline I/O Scheduler on BusyBox v1.16.1

Does anyone know how to add / make available the deadline I/O schedulers on BusyBox v1.16.1 ? The only two I see when I run "cat/sys/block/sda/queue/scheduler" is as follows: [noop] cfq My ...
10
votes
2answers
2k views

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 ...
-3
votes
1answer
111 views

Cloud server running slow

Can anyone help with this: One of our cloud servers is running slow and after running iotop I've noticed the below command running for nearly 2 hours, but I'm the only one who would run commands on ...
3
votes
0answers
364 views

what is snmp mib for getting NFS IO counters?

I can get local disk I/O requests and read/write bytes using the following snmp MIB: SNMP table: UCD-DISKIO-MIB::diskIOTable diskIOIndex diskIODevice diskIONRead diskIONWritten diskIOReads ...
5
votes
2answers
931 views

Tuning sequential disk reads for performance

I am reading a large file sequentially from the disk and trying to understand the iostat output while the reading is taking place. Size of the file : 10 GB Read Buffer : 4 KB Read ahead (/sys/block/...