{"id":825,"date":"2012-09-17T04:30:02","date_gmt":"2012-09-17T10:30:02","guid":{"rendered":"http:\/\/blog.supportpro.com\/?p=825"},"modified":"2026-01-09T05:51:05","modified_gmt":"2026-01-09T11:51:05","slug":"load-caused-by-raid-process","status":"publish","type":"post","link":"https:\/\/www.supportpro.com\/blog\/load-caused-by-raid-process\/","title":{"rendered":"Load caused by raid process"},"content":{"rendered":"

A sudden increase in server load can be alarming, especially on production systems. One common and often misunderstood cause is an active RAID resync or rebuild process<\/strong>. When a RAID array is rebuilding, the system performs intensive disk I\/O operations, which can significantly impact overall server performance.<\/p>\n

Understanding how to identify and safely manage RAID rebuild load is essential for Linux administrators.<\/p>\n

Identifying RAID Rebuild Activity<\/h3>\n

The first step when investigating unexplained load spikes on a Linux server is to check the RAID status using the following command:<\/p>\n

\n
\n
\n
<\/div>\n<\/div>\n<\/div>\n
cat<\/span> \/proc\/mdstat
\n<\/code><\/div>\n<\/div>\n

This file provides real-time information about all active software RAID arrays. If a rebuild or resync is in progress, you may see output similar to:<\/p>\n

\n
\n
\n
<\/div>\n<\/div>\n<\/div>\n
md0 : active raid1 sda4[0<\/span>] sdb4[1<\/span>]
\n482359552<\/span> blocks [2<\/span>\/2<\/span>] [UU]
\nresync = 58.7<\/span>% (283626752<\/span>\/482359552<\/span>) finish=376.7<\/span>min speed=8789<\/span>K\/sec
\n<\/code><\/div>\n<\/div>\n

The resync<\/code> line clearly indicates that the RAID array is rebuilding. The percentage, estimated completion time, and current speed help determine how much system load the process is generating.<\/p>\n

Why RAID Rebuilds Increase Server Load<\/h3>\n

During a RAID rebuild, large volumes of data are read and written continuously across disks. This causes:<\/p>\n