thr3ads.net - Gluster users - [Gluster-users] understanding dht value [Nov 2016]

If this information is useful, please help other people find it:
Share via:

Joe Julian

2016-Nov-08 19:05 UTC

[Gluster-users] understanding dht value

Here's an article explaining how dht works. The hash maps are per-directory.

https://joejulian.name/blog/dht-misses-are-expensive/


On 11/08/2016 11:04 AM, Ankireddypalle Reddy wrote:>
> Hi,
>
>        I am trying to make sense of the hash values that get 
> assigned/used by DHT.
>
>        /brick1/vol and /brick2/vol are the directories that are being 
> used as bricks in a distributed replicated volume.
>
> [root at glusterhackervm3 glus]# getfattr  -n trusted.glusterfs.dht -e 
> hex /brick1/vol
>
> getfattr: Removing leading '/' from absolute path names
>
> # file: brick1/vol
>
> trusted.glusterfs.dht=0x0000000100000000000000007ffffde1
>
> This means that any file gets hashed to a value from 0x00 to 
> 0x7ffffde1 gets stored on this brick.
>
> [root at glusterhackervm3 glus]# getfattr  -n trusted.glusterfs.dht -e 
> hex /brick2/vol
>
> getfattr: Removing leading '/' from absolute path names
>
> # file: brick2/vol
>
> trusted.glusterfs.dht=0x00000001000000007ffffde2ffffffff
>
> This means that any file that?s hashed to a value from 0x7ffffde2 to 
> 0xffffffff gets stored on this brick.
>
> What is confusing is the dht values that are shown for the directories 
> inside these brick directories. What do the dht values associated with 
> the sub directories signify.
>
> [root at glusterhackervm3 glus]# getfattr  -n trusted.glusterfs.dht -e 
> hex /brick2/vol/d/
>
> getfattr: Removing leading '/' from absolute path names
>
> # file: brick2/vol/d/
>
> trusted.glusterfs.dht=0x0000000100000000000000007ffffffe
>
> [root at glusterhackervm3 glus]# getfattr  -n trusted.glusterfs.dht -e 
> hex /brick2/vol/d/e
>
> getfattr: Removing leading '/' from absolute path names
>
> # file: brick2/vol/d/e
>
> trusted.glusterfs.dht=0x0000000100000000000000007ffffffe
>
> [root at glusterhackervm3 glus]# getfattr  -n trusted.glusterfs.dht -e 
> hex /brick2/vol/d/f
>
> getfattr: Removing leading '/' from absolute path names
>
> # file: brick2/vol/d/f
>
> trusted.glusterfs.dht=0x00000001000000007fffffffffffffff
>
> Thanks and Regards,
>
> Ram
>
> ***************************Legal Disclaimer***************************
> "This communication may contain confidential and privileged material 
> for the
> sole use of the intended recipient. Any unauthorized review, use or 
> distribution
> by others is strictly prohibited. If you have received the message by 
> mistake,
> please advise the sender by reply email and delete the message. Thank 
> you."
> **********************************************************************
>
>
> _______________________________________________
> Gluster-users mailing list
> Gluster-users at gluster.org
> http://www.gluster.org/mailman/listinfo/gluster-users
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://www.gluster.org/pipermail/gluster-users/attachments/20161108/13f5bef4/attachment.html>

Ankireddypalle Reddy

2016-Nov-08 19:23 UTC

head link

[Gluster-users] understanding dht value

Thanks for pointing to the article. I have been following the article all the
way.  What intrigues me is the dht values associated with sub directories.

[root at glusterhackervm3 glus]# getfattr  -n trusted.glusterfs.dht -e hex
/brick2/vol
getfattr: Removing leading '/' from absolute path names
# file: brick2/vol
trusted.glusterfs.dht=0x00000001000000007ffffde2ffffffff

[root at glusterhackervm3 glus]# getfattr  -n trusted.glusterfs.dht -e hex
/brick2/vol/d/
getfattr: Removing leading '/' from absolute path names
# file: brick2/vol/d/
trusted.glusterfs.dht=0x0000000100000000000000007ffffffe

Does it mean that only files whose DHT value ranges from 0x00 to 0x7ffffffe can
be saved inside the 'd' directory. But then it provides a very narrow
range of 0x7ffffde2 to  0x7ffffffe to be created in that directory.

Thanks and Regards,
Ram

From: gluster-users-bounces at gluster.org [mailto:gluster-users-bounces at
gluster.org] On Behalf Of Joe Julian
Sent: Tuesday, November 08, 2016 2:06 PM
To: gluster-users at gluster.org
Subject: Re: [Gluster-users] understanding dht value


Here's an article explaining how dht works. The hash maps are per-directory.

https://joejulian.name/blog/dht-misses-are-expensive/

On 11/08/2016 11:04 AM, Ankireddypalle Reddy wrote:
Hi,
       I am trying to make sense of the hash values that get assigned/used by
DHT.
       /brick1/vol and /brick2/vol are the directories that are being used as
bricks in a distributed  replicated volume.

[root at glusterhackervm3 glus]# getfattr  -n trusted.glusterfs.dht -e hex
/brick1/vol
getfattr: Removing leading '/' from absolute path names
# file: brick1/vol
trusted.glusterfs.dht=0x0000000100000000000000007ffffde1
This means that any file gets hashed to a value from 0x00 to 0x7ffffde1 gets
stored on this brick.


[root at glusterhackervm3 glus]# getfattr  -n trusted.glusterfs.dht -e hex
/brick2/vol
getfattr: Removing leading '/' from absolute path names
# file: brick2/vol
trusted.glusterfs.dht=0x00000001000000007ffffde2ffffffff
This means that any file that's hashed to a value from 0x7ffffde2 to
0xffffffff gets stored on this brick.


What is confusing is the dht values that are shown for the directories inside
these brick directories. What do the dht values associated with the sub
directories signify.

[root at glusterhackervm3 glus]# getfattr  -n trusted.glusterfs.dht -e hex
/brick2/vol/d/
getfattr: Removing leading '/' from absolute path names
# file: brick2/vol/d/
trusted.glusterfs.dht=0x0000000100000000000000007ffffffe

[root at glusterhackervm3 glus]# getfattr  -n trusted.glusterfs.dht -e hex
/brick2/vol/d/e
getfattr: Removing leading '/' from absolute path names
# file: brick2/vol/d/e
trusted.glusterfs.dht=0x0000000100000000000000007ffffffe


[root at glusterhackervm3 glus]# getfattr  -n trusted.glusterfs.dht -e hex
/brick2/vol/d/f
getfattr: Removing leading '/' from absolute path names
# file: brick2/vol/d/f
trusted.glusterfs.dht=0x00000001000000007fffffffffffffff

Thanks and Regards,
Ram
***************************Legal Disclaimer***************************
"This communication may contain confidential and privileged material for
the
sole use of the intended recipient. Any unauthorized review, use or distribution
by others is strictly prohibited. If you have received the message by mistake,
please advise the sender by reply email and delete the message. Thank you."
**********************************************************************



_______________________________________________

Gluster-users mailing list

Gluster-users at gluster.org<mailto:Gluster-users at gluster.org>

http://www.gluster.org/mailman/listinfo/gluster-users

***************************Legal Disclaimer***************************
"This communication may contain confidential and privileged material for
the
sole use of the intended recipient. Any unauthorized review, use or distribution
by others is strictly prohibited. If you have received the message by mistake,
please advise the sender by reply email and delete the message. Thank you."
**********************************************************************
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://www.gluster.org/pipermail/gluster-users/attachments/20161108/5c743262/attachment.html>

Gluster users - Nov 2016 - understanding dht value

[Gluster-users] understanding dht value

[Gluster-users] understanding dht value