Why am i getting Very slow dd dsync test results in Linux
I am investigating slow application issues with some New Hardware and am running into some odd results. I am trying to determine what is causing this behavior.
I am using
dd if=x.b1 of=x.b10 bs=8192 oflag=dsync
of a 101MB file simulate how our database is writing to disk (the dsync flag was suggested by our database vendor), and while normal dd commands without the dsync option are showing 80-100 Mb/s, with the dsync command I am getting results in the 160Kb/s-200Kb/s range.
This behavior has been viewed on multiple pieces of hardware, as well as different model hard drives and doing a drive wipe test
dd if=/dev/zero of=/dev/sda bs=8192 oflag=dsync
shows more expected 80-100Mb/s speed, which seems to suggest it is something in our custom OS that is slowing things down. We have run these tests under a custom SuseLinux as well as OracleOS (32 and 64 bit) and we continue to see these very low numbers.
Can you give me some ideas of where the problem is?
linux hard-drive performance dd
edited Jan 9 at 12:45
Jaywalker
1054
asked Jul 22 '15 at 16:19
azith28azith28
112
add a comment |
I am investigating slow application issues with some New Hardware and am running into some odd results. I am trying to determine what is causing this behavior.
I am using
dd if=x.b1 of=x.b10 bs=8192 oflag=dsync
of a 101MB file simulate how our database is writing to disk (the dsync flag was suggested by our database vendor), and while normal dd commands without the dsync option are showing 80-100 Mb/s, with the dsync command I am getting results in the 160Kb/s-200Kb/s range.
This behavior has been viewed on multiple pieces of hardware, as well as different model hard drives and doing a drive wipe test
dd if=/dev/zero of=/dev/sda bs=8192 oflag=dsync
shows more expected 80-100Mb/s speed, which seems to suggest it is something in our custom OS that is slowing things down. We have run these tests under a custom SuseLinux as well as OracleOS (32 and 64 bit) and we continue to see these very low numbers.
Can you give me some ideas of where the problem is?
linux hard-drive performance dd
edited Jan 9 at 12:45
Jaywalker
1054
asked Jul 22 '15 at 16:19
azith28azith28
112
add a comment |
I am investigating slow application issues with some New Hardware and am running into some odd results. I am trying to determine what is causing this behavior.
I am using
dd if=x.b1 of=x.b10 bs=8192 oflag=dsync
of a 101MB file simulate how our database is writing to disk (the dsync flag was suggested by our database vendor), and while normal dd commands without the dsync option are showing 80-100 Mb/s, with the dsync command I am getting results in the 160Kb/s-200Kb/s range.
This behavior has been viewed on multiple pieces of hardware, as well as different model hard drives and doing a drive wipe test
dd if=/dev/zero of=/dev/sda bs=8192 oflag=dsync
shows more expected 80-100Mb/s speed, which seems to suggest it is something in our custom OS that is slowing things down. We have run these tests under a custom SuseLinux as well as OracleOS (32 and 64 bit) and we continue to see these very low numbers.
Can you give me some ideas of where the problem is?
linux hard-drive performance dd
edited Jan 9 at 12:45
Jaywalker
1054
asked Jul 22 '15 at 16:19
azith28azith28
112
I am investigating slow application issues with some New Hardware and am running into some odd results. I am trying to determine what is causing this behavior.
I am using
dd if=x.b1 of=x.b10 bs=8192 oflag=dsync
of a 101MB file simulate how our database is writing to disk (the dsync flag was suggested by our database vendor), and while normal dd commands without the dsync option are showing 80-100 Mb/s, with the dsync command I am getting results in the 160Kb/s-200Kb/s range.
This behavior has been viewed on multiple pieces of hardware, as well as different model hard drives and doing a drive wipe test
dd if=/dev/zero of=/dev/sda bs=8192 oflag=dsync
shows more expected 80-100Mb/s speed, which seems to suggest it is something in our custom OS that is slowing things down. We have run these tests under a custom SuseLinux as well as OracleOS (32 and 64 bit) and we continue to see these very low numbers.
Can you give me some ideas of where the problem is?
linux hard-drive performance dd
linux hard-drive performance dd
edited Jan 9 at 12:45
Jaywalker
1054
asked Jul 22 '15 at 16:19
azith28azith28
112
edited Jan 9 at 12:45
Jaywalker
1054
asked Jul 22 '15 at 16:19
azith28azith28
112
edited Jan 9 at 12:45
Jaywalker
1054
edited Jan 9 at 12:45
Jaywalker
1054
edited Jan 9 at 12:45
Jaywalker
1054
1054
asked Jul 22 '15 at 16:19
azith28azith28
112
asked Jul 22 '15 at 16:19
azith28azith28
112
asked Jul 22 '15 at 16:19
azith28azith28
112
112
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
Specifying the oflag=dsync flag on dd which will dramatically slow down write speed to the output file.
From the dd manual:
dsync
Use synchronized I/O for data. For the output file, this forces a
physical write of output data on each write.
After every 8kb block, dd will wait for the data to be physically writen to the disk. This bypasses all caches including the hardware cache on the drive itself. The 8kb block will not start copying until this is complete.
If the copy speed is 200KB/s and the blocksize is 8k, then that's about 25 sync/s or 40ms a sync. This time is pretty typical for a hard drive.
The database vendor is probably asking you to try this because they use synchronized I/O for the transaction log of the database (to provide ACID reliability guarantees).
answered Jul 22 '15 at 17:38
Mikel RychliskiMikel Rychliski
33114
I'm familiar with why dsync is slower, but compared to what the vendor is telling us, it is much slower then it should be. why would the drive wipe dd tests show full speed with dsync but the copies show the very slow rate?
– azith28
Jul 22 '15 at 18:18
Do you have data=journal set in your mount options maybe? That would probably cause a journal write every 8k
– Mikel Rychliski
Jul 22 '15 at 21:37
No, this is not set in the mount table.
– azith28
Jul 23 '15 at 13:57
add a comment |
Your Answer
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "3"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fsuperuser.com%2fquestions%2f943952%2fwhy-am-i-getting-very-slow-dd-dsync-test-results-in-linux%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Specifying the oflag=dsync flag on dd which will dramatically slow down write speed to the output file.
From the dd manual:
dsync
Use synchronized I/O for data. For the output file, this forces a
physical write of output data on each write.
After every 8kb block, dd will wait for the data to be physically writen to the disk. This bypasses all caches including the hardware cache on the drive itself. The 8kb block will not start copying until this is complete.
If the copy speed is 200KB/s and the blocksize is 8k, then that's about 25 sync/s or 40ms a sync. This time is pretty typical for a hard drive.
The database vendor is probably asking you to try this because they use synchronized I/O for the transaction log of the database (to provide ACID reliability guarantees).
answered Jul 22 '15 at 17:38
Mikel RychliskiMikel Rychliski
33114
I'm familiar with why dsync is slower, but compared to what the vendor is telling us, it is much slower then it should be. why would the drive wipe dd tests show full speed with dsync but the copies show the very slow rate?
– azith28
Jul 22 '15 at 18:18
Do you have data=journal set in your mount options maybe? That would probably cause a journal write every 8k
– Mikel Rychliski
Jul 22 '15 at 21:37
No, this is not set in the mount table.
– azith28
Jul 23 '15 at 13:57
add a comment |
Specifying the oflag=dsync flag on dd which will dramatically slow down write speed to the output file.
From the dd manual:
dsync
Use synchronized I/O for data. For the output file, this forces a
physical write of output data on each write.
After every 8kb block, dd will wait for the data to be physically writen to the disk. This bypasses all caches including the hardware cache on the drive itself. The 8kb block will not start copying until this is complete.
If the copy speed is 200KB/s and the blocksize is 8k, then that's about 25 sync/s or 40ms a sync. This time is pretty typical for a hard drive.
The database vendor is probably asking you to try this because they use synchronized I/O for the transaction log of the database (to provide ACID reliability guarantees).
answered Jul 22 '15 at 17:38
Mikel RychliskiMikel Rychliski
33114
I'm familiar with why dsync is slower, but compared to what the vendor is telling us, it is much slower then it should be. why would the drive wipe dd tests show full speed with dsync but the copies show the very slow rate?
– azith28
Jul 22 '15 at 18:18
Do you have data=journal set in your mount options maybe? That would probably cause a journal write every 8k
– Mikel Rychliski
Jul 22 '15 at 21:37
No, this is not set in the mount table.
– azith28
Jul 23 '15 at 13:57
add a comment |
Specifying the oflag=dsync flag on dd which will dramatically slow down write speed to the output file.
From the dd manual:
dsync
Use synchronized I/O for data. For the output file, this forces a
physical write of output data on each write.
After every 8kb block, dd will wait for the data to be physically writen to the disk. This bypasses all caches including the hardware cache on the drive itself. The 8kb block will not start copying until this is complete.
If the copy speed is 200KB/s and the blocksize is 8k, then that's about 25 sync/s or 40ms a sync. This time is pretty typical for a hard drive.
The database vendor is probably asking you to try this because they use synchronized I/O for the transaction log of the database (to provide ACID reliability guarantees).
answered Jul 22 '15 at 17:38
Mikel RychliskiMikel Rychliski
33114
Specifying the oflag=dsync flag on dd which will dramatically slow down write speed to the output file.
From the dd manual:
dsync
Use synchronized I/O for data. For the output file, this forces a
physical write of output data on each write.
After every 8kb block, dd will wait for the data to be physically writen to the disk. This bypasses all caches including the hardware cache on the drive itself. The 8kb block will not start copying until this is complete.
If the copy speed is 200KB/s and the blocksize is 8k, then that's about 25 sync/s or 40ms a sync. This time is pretty typical for a hard drive.
The database vendor is probably asking you to try this because they use synchronized I/O for the transaction log of the database (to provide ACID reliability guarantees).
answered Jul 22 '15 at 17:38
Mikel RychliskiMikel Rychliski
33114
answered Jul 22 '15 at 17:38
Mikel RychliskiMikel Rychliski
33114
answered Jul 22 '15 at 17:38
Mikel RychliskiMikel Rychliski
33114
answered Jul 22 '15 at 17:38
Mikel RychliskiMikel Rychliski
33114
33114
I'm familiar with why dsync is slower, but compared to what the vendor is telling us, it is much slower then it should be. why would the drive wipe dd tests show full speed with dsync but the copies show the very slow rate?
– azith28
Jul 22 '15 at 18:18
Do you have data=journal set in your mount options maybe? That would probably cause a journal write every 8k
– Mikel Rychliski
Jul 22 '15 at 21:37
No, this is not set in the mount table.
– azith28
Jul 23 '15 at 13:57
add a comment |
I'm familiar with why dsync is slower, but compared to what the vendor is telling us, it is much slower then it should be. why would the drive wipe dd tests show full speed with dsync but the copies show the very slow rate?
– azith28
Jul 22 '15 at 18:18
Do you have data=journal set in your mount options maybe? That would probably cause a journal write every 8k
– Mikel Rychliski
Jul 22 '15 at 21:37
No, this is not set in the mount table.
– azith28
Jul 23 '15 at 13:57
I'm familiar with why dsync is slower, but compared to what the vendor is telling us, it is much slower then it should be. why would the drive wipe dd tests show full speed with dsync but the copies show the very slow rate?
– azith28
Jul 22 '15 at 18:18
I'm familiar with why dsync is slower, but compared to what the vendor is telling us, it is much slower then it should be. why would the drive wipe dd tests show full speed with dsync but the copies show the very slow rate?
– azith28
Jul 22 '15 at 18:18
Do you have data=journal set in your mount options maybe? That would probably cause a journal write every 8k
– Mikel Rychliski
Jul 22 '15 at 21:37
Do you have data=journal set in your mount options maybe? That would probably cause a journal write every 8k
– Mikel Rychliski
Jul 22 '15 at 21:37
No, this is not set in the mount table.
– azith28
Jul 23 '15 at 13:57
No, this is not set in the mount table.
– azith28
Jul 23 '15 at 13:57
add a comment |
Thanks for contributing an answer to Super User!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fsuperuser.com%2fquestions%2f943952%2fwhy-am-i-getting-very-slow-dd-dsync-test-results-in-linux%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
