All Questions
Tagged with performance io
99
questions
154
votes
13
answers
75k
views
Are networks now faster than disks?
This is a software design question
I used to work on the following rule for speed
cache memory > memory > disk > network
With each step being 5-10 times the previous step (e.g. cache ...
- 1,635
39
votes
5
answers
81k
views
How to identify I/O bottlenecks on a Linux server?
How do you determine that the performance of your Linux server is I/O bound and, perhaps more importantly, what process or processes are casuing the problem?
- 10k
21
votes
1
answer
38k
views
Determining which process is causing heavy disk I/O?
I've seen this question:
How to identify heavy write to disk?
And I've used dstat and atop before...but they don't seem to pinpoint what process is causing disk I/O. For example, from dstat:
dstat ...
- 1,729
21
votes
2
answers
35k
views
jbd2/dm-0-8 consuming all I/O
What is jbd2/dm-0-8 and why It is consuming all my I/O usage and causing I/O wait?
Is there anyway to disable this?
Bonnie++ results: http://pastebin.com/iQCWP1qp
$ sudo hdparm -t /dev/sda1
/dev/...
- 355
14
votes
4
answers
3k
views
How do limit disc i/o during backup?
I have a cron that basically do a simple "tar zcf" in the night.
The server has:
8 Cores - Intel(R) Xeon(R) CPU E5606 @ 2.13GHz
25GB RAM
Ubuntu 12.04.2 LTS
Hardware RAID 1 (LSI Logic / Symbios ...
- 253
12
votes
2
answers
5k
views
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, ...
- 3,110
11
votes
4
answers
12k
views
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 ...
- 111
10
votes
6
answers
14k
views
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 ...
- 1,744
10
votes
2
answers
10k
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 ...
- 131
9
votes
2
answers
4k
views
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 ...
- 905
9
votes
2
answers
8k
views
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 ...
- 273
8
votes
4
answers
22k
views
Flush-0:n processes causing massive bottleneck
I have a LAMP cluster that shares files via NFS and occasionally one of them will be stricken for a while when mysterious flush processes start appearing.
Can anyone help me? The only way to resolve ...
- 731
8
votes
2
answers
19k
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 ...
- 233
7
votes
1
answer
2k
views
How efficient is the tac command on large files
The taccommand (catreversed) can be used to read a file backwards, just like cat reads it rom the beginning. I wonder, how efficient this is. Does it have to read the whole file from the beginning and ...
- 314
6
votes
6
answers
8k
views
Find the bottleneck: disk I/O on Windows XP
One of our development boxes has developed a problem wherein performance will occasionally drop through the floor. When this happens, you can hear the hard drive thrashing, but I don't know what's ...
- 195
6
votes
1
answer
214
views
How to prevent IO Load under Linux for Video serving?
I'm currently serving videos of conferences via Nginx on 3 servers; 4 cores, enough memory (no swap used) and RAID-10 with 8 drives per server. Unfortunately iostat -xd 1 gives me 100% on all 3 ...
- 229
6
votes
1
answer
917
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 : [...
- 304
6
votes
3
answers
5k
views
Massive performance degradation on sustained sequential write
I'm in the process of migrating data into LUKS partitions. Now that the operating system drive is running off LUKS, I tried to start migrating the data drives. Then the server stopped responding.
...
- 314
5
votes
1
answer
3k
views
Linux Read-Ahead Downsides
Are there any downsides to raising the size of the read-ahead cache?
On our farm, we're currently running at 256, and upon raising that higher, we are seeing significant throughput gains.
[root@...
- 285
5
votes
1
answer
790
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 ...
- 161
5
votes
2
answers
2k
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/...
- 283
4
votes
3
answers
10k
views
High Load - Low IO - Low CPU usage
I have a system whose load is rather high. As you can see from the top output below, CPU usage and I/O is negligible:
top - 17:31:59 up 4 days, 2:34, 2
users, load average: 1.00, 0.99, 1.00
Tasks:...
- 51
4
votes
1
answer
6k
views
Filesystem Performance for LUKS Encrypted Volumes?
As you can format a LUKS volume with any filesystem you want, are certain filesystems better-suited to IO performance against an encrypted filesystem? Specifically, I'm wondering about a loop device ...
- 1,157
4
votes
4
answers
6k
views
Disk performance below expectations
this is a follow-up to a previous question that I asked (Two servers with inconsistent disk speed).
I have a PowerEdge R510 server with a PERC H700 integrated RAID controller (call this Server B) ...
- 183
4
votes
3
answers
3k
views
Disk write speed much slower than read speed
I have a VPS server (WiredTree), running CentOS.
After experiencing some performance issues I created a simple benchmark for disk read/write speed using the following script:
echo Write to disk
dd ...
- 175
4
votes
1
answer
2k
views
Measuring Disk IO programmatically
I want to measure some numbers related to disk io in a given timespan, programmatically. This means I don't want to spawn a process like iostat to get my numbers, by prefer to read something from proc ...
- 844
4
votes
1
answer
2k
views
KVM bad IO sync performance in Linux guest
I'm setting up virtualized Ubuntu 15.10 guest inside Ubuntu 15.04 server using libvirt and KVM.
Storage in host system:
# mount | grep ext4
/dev/sda1 on / type ext4 (rw,relatime,errors=remount-ro,...
- 141
4
votes
1
answer
2k
views
High disk time on SQL Server
We have a dedicated SQL Server 2008 R2 Enterprise Edition.
The setup is:
D: (data files) - stored on local ssd disks (not the same disks as log files) (raid 10)
E: (log files) - stored on local ssd ...
- 51
4
votes
0
answers
2k
views
Why are pgpgin/s and majflt/s inconsistent in sar -B?
In sar -B ouptut, I would naively expect pgpgin/s to equal majflt/s multiplied by the system page size. From man sar:
pgpgin/s
Total number of kilobytes the system paged in ...
- 141
3
votes
3
answers
23k
views
High await in sar
My database server has the following sar output for the data device:
[postgres@dbsrv07 ~]$ LC_ALL=POSIX sar -d |egrep "await|dev253-2"
00:00:01 DEV tps rd_sec/s wr_sec/s avgrq-sz ...
- 151
3
votes
2
answers
16k
views
Determining cause of high NFS/IO utilization without iotop
I have a server that is doing an NFSv4 export for user's home directories. There are roughly 25 users (mostly developers/analysts) and about 40 servers mounting the home directory export. ...
- 1,047
3
votes
4
answers
3k
views
Azure IO performance
We have a number of Windows Server virtual machines that we use for .NET and Java development and QA. I find Azure attractive for the obvious reasons but mainly for the opportunity to reduce non-...
- 131
3
votes
1
answer
4k
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/...
- 170
3
votes
2
answers
2k
views
Disk IO Rate: What causes it and what does it mean to me?
I just got a mail from Linode saying that my account "has exceeded the notification threshold (1000) for disk io rate by averaging 1017.36 for the last 2 hours. "
My question is just out of curious:
...
- 199
3
votes
6
answers
20k
views
Show IO on Netapp
I think I might be hitting the IO limits of what my Netapp can deliver, as I have been adding more servers to my cluster and iowait has gone up on each server.
However, how do I quantify this? How ...
- 2,273
3
votes
2
answers
4k
views
How iostat figures out to take CPU idle time to consider as %idle or %iowait?
I was going through iostat man page. According to it,
%iowait
Show the percentage of time that the CPU or CPUs were idle during which the system
had an outstanding disk I/O request.
%idle
...
- 2,748
3
votes
2
answers
881
views
How does I/O performance on Intel E5 procs change with and without QPI
I am in the process of specifying a low-mid range server (which we will purchase multiples of). The application is essentially a software router, so it is very NIC-based I/O intensive. Processor ...
- 539
3
votes
1
answer
446
views
IO related performance bottleneck on a LAMP server
I am administering a big LAMP server with some thousand users. About a week ago, things slowed down, and the only thing I see that the IO latency is increased dramatically. Users experience slow page ...
- 85
3
votes
1
answer
1k
views
Quantifying the effects of partition mis-alignment
I'm experiencing some significant performance issues on an NFS server. I've been reading up a bit on partition alignment, and I think I have my partitions mis-aligned. I can't find anything that ...
- 1,047
3
votes
1
answer
1k
views
Limited I/O Performance in Dell T410
We have a small number of Dell T410 and T710 systems. Each has a Dell SAS 6iR controller with 6 SATAII disks, 1x160GB OS and 5x3TB DATA disks. We have been having disk access speed issues all along, ...
- 31
3
votes
1
answer
988
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,...
- 2,655
3
votes
0
answers
54
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 ...
- 83
2
votes
2
answers
4k
views
VMWare Esxi Looking for Bottlenecks
I have a VMWare ESxi box, 22GB ram, Dual Quad Core Xeon, 2 Sas drives + Write caching raid controller etc.
Anyways, have about 30 small XP VM's running on it and starting to get some very slow boot ...
- 233
2
votes
1
answer
5k
views
Poor guest I/O performance KVM Ubuntu 12.04
I have a guest VM running inside a 12.04 Ubuntu host. VM was created using the vmbuilder python script.
On the host the phoronix-test-suite "aio-stress" gives a performance speed of >1600MB/s Random ...
- 21
2
votes
4
answers
8k
views
How to reduce mysql disk io?
mysql> explain SELECT *
-> FROM (`items`)
-> WHERE `states` = 'A'
-> ORDER BY `updated_date` desc
-> LIMIT 20520, 40;
+----+-------------+--------+--------+--------------...
- 151
2
votes
1
answer
404
views
About IOPS of a RAID5 disk array without cache
we are using a 530-8i RAID adapter,which is none-cache supported, on a Lenovo ThinkSystem SR590 server.And we have 4 HDD(600GB/10K RPM/SAS) in the array.
I read an article about calculating the disk/...
- 21
2
votes
2
answers
4k
views
Does a read on a NFS file system slow performance?
If a NFS client reads a file, does any network traffic happen? or is it just writes (by any node) that result in network traffic?
In particular, I'm interested in whether doing a file_exists() call ...
- 4,297
2
votes
3
answers
7k
views
RAID10 without write-back cache = horrible write performance?
I have just provisioned a dedicated server on singlehop.
I'm running it through some tests to know what to expect performance-wise. On the I/O side (with 4 1TB disks in RAID 10) I get:
write-cache ...
- 133
2
votes
3
answers
509
views
Analysing Disk IO Traffic
I am running a web server (Ubuntu 11.04) that exhibits unexpected high write traffic. When the server is not supposed to write at all, the amount of write traffic is comparable to the read traffic.
...
- 123
2
votes
1
answer
104
views
MYSQL vs. InnoDB [closed]
mysqltuner output.
-------- Storage Engine Statistics -----------------------------------------------------------------
[--] Status: +ARCHIVE +BLACKHOLE +CSV -FEDERATED +InnoDB +MEMORY +MRG_MYISAM +...
