[Gluster-users] understanding dht value

[Joe Julian]

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
>
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