[DOCS-205] Linux Software Raid Bitmap Configuration Created: 16/May/12  Updated: 30/Oct/23  Resolved: 27/Jul/16

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

Type: Task Priority: Minor - P4
Reporter: Mathias Stearn Assignee: Unassigned
Resolution: Won't Fix Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Participants:
Days since reply: 7 years, 29 weeks ago

 Description   

The bitmap option with Linux Software Raid (i.e. md) is dangerous when used with MongoDB.

To figure out if you're using bitmap, see bitmap in /proc/mdstat that the raid array was set up with this
feature.

While "bitmap" can improve recovery time for large RAID arrays, it can have disastrous effects on write performance because it needs to update the bitmap before it can do any write. This is particularly problematic when using journaling.

This can potentially double the IOPS requirements (tripling if you need to read-modify-write the bitmap.) It also means that otherwise sequential I/O becomes non-sequential. To disable bitmap use the mdadm /dev/mdX --grow --bitmap none command.

Immediately after disabiling bitmap, the io utilization on the server will reduce and throughput will stabilize.



 Comments   
Comment by Emily Hall [ 27/Jul/16 ]

Closed by Emily Hall for Housekeeping on 7/27/16.
Please create a new ticket if for prioritization.

Thank you!

Generated at Thu Feb 08 07:38:10 UTC 2024 using Jira 9.7.1#970001-sha1:2222b88b221c4928ef0de3161136cc90c8356a66.