Visit Our UNIX and Linux User Community


data from blktrace: read speed V.S. write speed


 
Thread Tools Search this Thread
Special Forums Hardware Filesystems, Disks and Memory data from blktrace: read speed V.S. write speed
# 1  
Old 10-26-2009
data from blktrace: read speed V.S. write speed

I analysed disk performance with blktrace and get some data:
read:
Code:
  8,3    4     2141     2.882115217  3342  Q   R 195732187 + 32 [cat]
  8,3    4     2142     2.882116411  3342  G   R 195732187 + 32 [cat]
  8,3    4     2144     2.882117647  3342  I   R 195732187 + 32 [cat]
  8,3    4     2145     2.882118965  3342  D   R 195732187 + 32 [cat]
  8,3    4     2149     2.884145702     0  C   R 195732187 + 32 [0]

write:
Code:
  
  8,3    4    43622     5.305507398  3436  Q   W 17805895 + 8 [bash]
  8,3    4    43623     5.305508277  3436  G   W 17805895 + 8 [bash]
  8,3    4    43624     5.305508574  3436  I   W 17805895 + 8 [bash]
  8,3    2      414     5.306695591     0  D   W 17805895 + 16 [swapper]
  8,3    2      418     5.307020642     0  C   W 17805895 + 16 [0]

And, d2c time of one read request is 0.002026737s. On the other hand, d2c time of one write request is 0.000325051s. It show: read time > write time. Is it right? why? I have no idea.
# 2  
Old 10-26-2009
The write operations are almost certainly getting cached somewhere, most likely in the kernel page cache or the cache on the disk(s) themselves depending on your OS and hardware setup.

Previous Thread | Next Thread
Test Your Knowledge in Computers #735
Difficulty: Medium
The Commodore 64 was shipped with BASIC v2.0 in RAM.
True or False?

10 More Discussions You Might Find Interesting

1. UNIX for Advanced & Expert Users

How to read a fast written log file at Real time speed?

Hello All, I am building a real time parser for a log file in my application. The log file is continuously written at a very fast pace and gets rolled over every 10 minutes. I have measured the speed and observed that around 1000 lines are written to it every second, each line about 30-40... (7 Replies)
Discussion started by: cool.aquarian
7 Replies

2. Red Hat

Read speed too bad on NAS share on VM

Hi, We have two servers in scenario (vmsoldot01 is Oracle VM with Linux and tldtppod15 is physical Linux server). One NAS share is mounted on both servers with similar permissions and access. But READ speed is too bad on virtual in comparison to physical server. While trying to diagnose this, I... (2 Replies)
Discussion started by: solaris_1977
2 Replies

3. Shell Programming and Scripting

Speed Up Grep

Hi, I have to grep string from 20 - 30 files each carries 200 - 300 MB size and append to the file. How to speed the grepping time. cat catalina.out_2012_01_01 | grep "xxxxx" >> backup.txt PLZ, Suggest me, Regards, Nanthagopal A (5 Replies)
Discussion started by: nanthagopal
5 Replies

4. Hardware

Hardware Correction: How to change DVD write speed

I am now on Kernel 2.6.32-26 For me 16x CD write speed is okay. I have old hardware which was able to write DVDs at 1x, back in previous linux version. Now, I dont get speed of less than 4x. Tested on k3b, xfburn, and brasero. But all start at bottom 4x write speed. k3b forced back to... (0 Replies)
Discussion started by: makh
0 Replies

5. Filesystems, Disks and Memory

Disk read and write speed.

Being a novice user to linux i m little unaware of how would i check disk read write speed. One of my mate is suggesting to create a file using dd command and check how much time it takes to create a 30 gb file . I think this has a little sense however i would also like to take your reviews... (5 Replies)
Discussion started by: pinga123
5 Replies

6. Shell Programming and Scripting

How to speed up grep?

hi i'm greping the files with sepefic keyword, where the file is of too big. Assume there are 10 days log file each of more than 200mb. i've to grep all those files with a specific keywords. for example, 1. i'll grep for error message 2. after the i'll do one more grep for keyword... (4 Replies)
Discussion started by: vij_krr
4 Replies

7. Filesystems, Disks and Memory

Write Speed into a big file (in Gb's)

If a file size increases in Linux/UNIX to say in GB's then will there be a decrease in write speed. I mean will it take more time to write to a large file then to a small one?? Please clarify? Thanks in advance (2 Replies)
Discussion started by: anilgurwara
2 Replies

8. Filesystems, Disks and Memory

dmidecode, RAM speed = "Current Speed: Unknown"

Hello, I have a Supermicro server with a P4SCI mother board running Debian Sarge 3.1. This is the "dmidecode" output related to RAM info: RAM speed information is incomplete.. "Current Speed: Unknown", is there anyway/soft to get the speed of installed RAM modules? thanks!! Regards :)... (0 Replies)
Discussion started by: Santi
0 Replies

9. UNIX for Dummies Questions & Answers

Speed of mv vs. cp

Hi, Is mv (move) command quicker than cp (copy command)? I have large files and I want to know if mv actually copy the data to a new file then deletes the old or whether it just alters information the file system without physically moving data - Unfortuanately I don't have large files to test... (2 Replies)
Discussion started by: GMMike
2 Replies

10. UNIX for Dummies Questions & Answers

Speed it up!

I wonder, are there any "tricks" to increase my server's access time in general? (4 Replies)
Discussion started by: pappous
4 Replies

Featured Tech Videos