[Gluster-users] Heal operation detail of EC volumes

[Serkan Çoban]

Ok I understand that heal operation takes place on server side. In
this case I should see X KB
 out network traffic from 16 servers and 16X KB input traffic to the
failed brick server right? So that process will get 16 chunks
recalculate our chunk and write it to disk.
The problem is I am not seeing such kind of traffic on servers. In my
configuration (16+4 EC) I see 20 servers are all have 7-8MB outbound
traffic and none of them has more than 10MB incoming traffic.
Only heal operation is happening on cluster right now, no client/other
traffic. I see constant 7-8MB write to healing brick disk. So where is
the missing traffic?

On Tue, May 30, 2017 at 10:25 AM, Ashish Pandey <aspandey at redhat.com> wrote:
>
> When we say client side heal or server side heal, we basically talking about
> the side which "triggers" heal of a file.
>
> 1 - server side heal - shd scans indices and triggers heal
>
> 2 - client side heal - a fop finds that file needs heal and it triggers heal
> for that file.
>
> Now, what happens when heal gets triggered.
> In both  the cases following functions takes part -
>
> ec_heal => ec_heal_throttle=>ec_launch_heal
>
> Now ec_launch_heal just creates heal tasks (with ec_synctask_heal_wrap which
> calls ec_heal_do ) and put it into a queue.
> This happens on server and "syncenv" infrastructure which is nothing but a
> set of workers pick these tasks and execute it. That is when actual
> read/write for
> heal happens.
>
>
> ________________________________
> From: "Serkan Çoban" <cobanserkan at gmail.com>
> To: "Ashish Pandey" <aspandey at redhat.com>
> Cc: "Gluster Users" <gluster-users at gluster.org>
> Sent: Monday, May 29, 2017 6:44:50 PM
> Subject: Re: [Gluster-users] Heal operation detail of EC volumes
>
>
>>>Healing could be triggered by client side (access of file) or server side
>>> (shd).
>>>However, in both the cases actual heal starts from "ec_heal_do" function.
> If I do a recursive getfattr operation from clients, then all heal
> operation is done on clients right? Client read the chunks, calculate
> and write the missing chunk.
> And If I don't access files from client then SHD daemons will start
> heal and read,calculate,write the missing chunks right?
>
> In first case EC calculations takes places in client fuse process, in
> second case EC calculations will be made in SHD process right?
> Does brick process has any role in EC calculations?
>
> On Mon, May 29, 2017 at 3:32 PM, Ashish Pandey <aspandey at redhat.com> wrote:
>>
>>
>> ________________________________
>> From: "Serkan Çoban" <cobanserkan at gmail.com>
>> To: "Gluster Users" <gluster-users at gluster.org>
>> Sent: Monday, May 29, 2017 5:13:06 PM
>> Subject: [Gluster-users] Heal operation detail of EC volumes
>>
>> Hi,
>>
>> When a brick fails in EC, What is the healing read/write data path?
>> Which processes do the operations?
>>
>> Healing could be triggered by client side (access of file) or server side
>> (shd).
>> However, in both the cases actual heal starts from "ec_heal_do" function.
>>
>>
>> Assume a 2GB file is being healed in 16+4 EC configuration. I was
>> thinking that SHD deamon on failed brick host will read 2GB from
>> network and reconstruct its 100MB chunk and write it on to brick. Is
>> this right?
>>
>> You are correct about read/write.
>> The only point is that, SHD deamon on one of the good brick will pick the
>> index entry and heal it.
>> SHD deamon scans the .glusterfs/index directory and heals the entries. If
>> the brick went down while IO was going on, index will be present on killed
>> brick also.
>> However, if a brick was down and then you started writing on a file then
>> in
>> this case index entry would not be present on killed brick.
>> So even after brick will be  UP, sdh on that brick will not be able to
>> find
>> it out this index. However, other bricks would have entries and shd on
>> that
>> brick will heal it.
>>
>> Note: I am considering each brick on different node.
>>
>> Ashish
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
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>>
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