Patrol Read vs Consistency Check

Ale123,

The difference between the Patrol Read and the Consistency Check is that the Patrol Read check blocks on the drives, Consistency Check verifies the redundancy is the same across the Virtual Disk members. Specifically the

Patrol Read operates by default as an automated background task that checks all of the individual blocks on a hard drive to ensure that the data can be read correctly. Patrol Read will attempt to correct blocks that are bad or remap un-correctable blocks to reserved blocks.

Check Consistency is a manually activated (it can also be scheduled) function that compares all the drives in an array against each other to ensure that the data and redundancy correctly match.

Let me know if this helps.

In other words, patrol read can't replace a cosnistency check, but consistency check could replace a patrol read, because it does the same plus a consistency check for data. Right ?

I was already aware of this, but as consistency check should check ALL blocks on all disks, to verify the raid redundancy, this check should also detect any unreadable blocks, like patrol read does.

If I understood properly, patrol read is a "lighwheight" version of consistency check, because it doesn't check for data consistency, thus is lighter.

If you have to check for consistency, you still have to read all from every array member.........

"I was already aware of this, but as consistency check should check ALL blocks on all disks"

It should check all sectors, but it does not.

As to importance, it is the opposite...

And to add, a consistency check ONLY tests areas of the disks which contain data and parity, not unused areas of the arrays disks, a patrol read checks every sector of the involved disks. With todays larger disks the patrol read test is more important then a CC. Patrol reads find error in unused areas of the disks involved which are not normally found until the unused areas are written to or tested. Now, if enough areas are read/written to in a short period of time, and a threshold of bad  areas are found, the raid will fail, especially during a rebuild.

The Consistency check tool  was developed in a time when disk were expected to grow to less then a hundred megabytes. Patrol reads came much latter, as the disks became much larger and raid failures were increasing, primarily during rebuilds. As to the power of each tool, Patrol Reads does most of what a CC does, an inconsistency due to a faulty read/write/or disk error will be found by a PR. As is a consistency errors not caused by a physical disk error is rare, over all consistency errors are very rare (my experience), physical sector errors are far more common. Personally unless a server is used 24/7, I run a scheduled .bat to run  both a CC and a Patrol Read for once a week during off hours.