What are barriers and do I really need them to be enabled?

[stefeman]

I heard they make huge difference in speed depending on if they are enabled or not.

I'm looking into following choices:

2x2TB RAID1 Barriers enabled = (Slow as hell system for multiple VM's/CT's)?
2x2TB RAID1 Barries Disabled = (Faster)??
2x2TB RAID0 Barries Disabled = (Ultra Fast)?

Data redundancy is not a must as the drives will be brand new, and I have nothing critical installed + I have regular backups.

What I'm comparing is mainly RAID1 with no barriers VS RAID0 with no barriers. Is the difference much between them? To know this I'd wish to know how exactly barriers work? Could anyone care to explain it's functionality with simple terms?

As for the cache, I intend to use writeback mode.

Thank you in advance.

 

[mir]

RAID0 is not raid at all. Loose one disk and all your data is lost on both disks. If you are using ext4 go for barrier disabled. With recent ext4 and default mount option 'data=ordered' there is no difference between barrier enabled or not except for the performance penalty. This is my personal opinion from almost 10 years use of ext4, Others my have other opinions. YMMW.

 

[dcsapak]

If you are using ext4 go for barrier disabled. With recent ext4 and default mount option 'data=ordered' there is no difference between barrier enabled or not except for the performance penalty. This is my personal opinion from almost 10 years use of ext4, Others my have other opinions. YMMW.

this is only true if your disks are battery backed
see the relevant part of the kernel documentation
(https://www.kernel.org/doc/Documentation/filesystems/ext4.txt)

Write barriers enforce proper on-disk ordering
of journal commits, making volatile disk write caches
safe to use, at some performance penalty. If
your disks are battery-backed in one way or another,
disabling barriers may safely improve performance.

 

[mir]

this is only true if your disks are battery backed
see the relevant part of the kernel documentation
(https://www.kernel.org/doc/Documentation/filesystems/ext4.txt)

I know the documentation but this is only cover my ass statements with no known proof from the trenches in the real world. I have had my share off power cuts from disks and never, to my knowledge, lost a bit.