Re: understanding dht value

Ankireddypalle Reddy <areddy@xxxxxxxxxxxxx> · Tue, 8 Nov 2016 19:23:48 +0000

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@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@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@xxxxxxxxxxx [mailto:gluster-users-bounces@xxxxxxxxxxx]
On Behalf Of Joe Julian

Sent: Tuesday, November 08, 2016 2:06 PM

To: gluster-users@xxxxxxxxxxx

Subject: Re:  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@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@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@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@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@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

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