[DOCS-5329] Warn about archiveMovedChunks disk consumption when adding shards Created: 01/May/15  Updated: 30/Oct/23  Resolved: 22/Jun/15

Status: Closed
Project: Documentation
Component/s: manual
Affects Version/s: None
Fix Version/s: Server_Docs_20231030

Type: Task Priority: Minor - P4
Reporter: Akira Kurogane Assignee: Kay Kim (Inactive)
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
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Participants:
Days since reply: 8 years, 34 weeks, 2 days ago

 Description   

Related page: /tutorial/add-shards-to-shard-cluster/

I recently found out about the behaviour of the sharding.archiveMovedChunks option (still on by default) when I helped someone add a new shard.

The simplified case: There is a 2-shard cluster with 1 TB on each shard, but the disks were almost full (only 100GB of disk space left). Adding a third shard stopped the increase in db storage (and disk space) and all seemed well. But the disk usage increased on the older shards, quickly, as the balancer moved chunks to the other shards. In a well-balanced cluster each of the original two shards was in the process of migrating 330GB off and making movechunk archives of the same size. If the issue hadn't been noticed in time a disk-full error would have happened.

I had heard of the sharding.archiveMovedChunks (a.k.a. --moveParanoia) but didn't realize it would be on by default. That the migrated chunk's data was being saved outside of the extent files and consuming more diskspace was a real gotcha. As adding shards is something you often do to relieve disk space please add a warning explaining this in the addShard documentation.



 Comments   
Comment by Akira Kurogane [ 23/Jun/15 ]

Thanks Kay!

Comment by Githook User [ 22/Jun/15 ]

Author:

{u'username': u'kay-kim', u'name': u'kay', u'email': u'kay.kim@10gen.com'}

Message: DOCS-5629 DOCS-5329 include archiveMovedChunks behavior in the chunk migration
Branch: master
https://github.com/mongodb/docs/commit/a5a6c9a86fc410c32d3c0671868ef011c36a4740

Comment by Githook User [ 22/Jun/15 ]

Author:

{u'username': u'kay-kim', u'name': u'kay', u'email': u'kay.kim@10gen.com'}

Message: DOCS-5629 DOCS-5329 include archiveMovedChunks behavior in the chunk migration
Branch: v2.6
https://github.com/mongodb/docs/commit/1458f9f892041ba9b75457008b8b7e6fff01347e

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