[DOCS-7104] EXT4 and WT incompatibilities Created: 05/Feb/16  Updated: 30/Oct/23  Resolved: 18/Feb/20

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

Type: Task Priority: Critical - P2
Reporter: Osmar Olivo Assignee: Brian Lane
Resolution: Done Votes: 4
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Related
is related to SERVER-18314 Stall during fdatasync phase of check... Closed
is related to SERVER-22606 Startup warning if ext4 is used with ... Closed
Participants:
Days since reply: 3 years, 48 weeks, 5 days ago
Story Points: 0

 Description   

Currently we are lacking in a comprehensive explanation of the issues that can arise with WT when running on EXT4.

Specifically, details on what the issue is, under what conditions it can manifest, and what the symptoms are. We have similar pages explaining how NUMA or low ulimits can negatively impact a cluster, and therefore it makes sense to have a page covering EXT4's issue in a bit more detail.

Particularly since it is a widely accepted filesystem and the issues will only manifest themselves under certain conditions.



 Comments   
Comment by Nic Cottrell [ 06/Mar/20 ]

brian.lane - did you mean to close this DOCS ticket? If I understand the SERVER-181314 discussion correctly, it confirms that there is still EXT4 issues under heavy load. I still think a note in the docs along the line of josef.ahmad's last comment would help inform customers. Maybe something like:

> Performance testing has demonstrated that when the volume of IO requests exceed the storage throughput capacity, XFS degrades the throughput more gracefully, whereas ext4 continues "full on" until it stalls altogether. For most production use cases the graceful slowdown provides better application results.

Comment by Brian Lane [ 09/Oct/19 ]

Just dropping on a note on this issue in case people have not been watching SERVER-18314.

Some recent tests with RHEL 7.6 and MongoDB 4.0.12 and stalling still with EXT4.

-Brian

Comment by Joel Parke [X] [ 25/Apr/19 ]

It seems that this warning is so old, when the kernel for Ubuntu 19.04 is now 5.0, that forcing one to use XFS with WT, seems a bit lame.   Especially when the OLD stalls never did express exactly why or if later kernels had this issue.  

Is this simply because in production, NO ONE is running XFS with WT with more modern kernels?

If so this is doing a huge disservice to mongodb.

If anyone has clear insight or experience with this issue, please comment!!!  

I never see this issue in my production system!  but I wouldn't expect to, since my files are small.

Comment by Aaron Queen [ 31/Aug/17 ]

Has there been any movement on this?

Most distros still ship with EXT4 as default, and it seems strange to strongly suggest using a specific file system for your data directory without the information needed to justify going through the hassle of partitioning off with XFS.

EXT4 and XFS both receive updates with new kernels as well, so is this problem specific to certain kernels under a specific version, or is it EXT4 in general, even on the very latest mainline kernel? This type of information would be very helpful, and could also possibly eliminate the startup warning if it is actually specifically EXT4 + kernel below a certain 2.x, 3.x, 4.x version.

Generated at Thu Feb 08 07:53:35 UTC 2024 using Jira 9.7.1#970001-sha1:2222b88b221c4928ef0de3161136cc90c8356a66.