How to know whether disks "handle flush requests correctly"
The btrfs wiki Main Page warns that "it is currently possible to corrupt a filesystem irrecoverably if your machine crashes or loses power on disks that don't handle flush requests correctly."
How do you know if this applies to your drives? Is there a way to test it, or a model list, or are newer SATA drives (magnetic, not SSDs) always ok? Does it depend on the controller? (I have a SiI 3114, latest BIOS.)
I would also be using btrfs on top of dm-crypt (with the latest release kernel). Some kernel versions ago, the message that write barriers aren't supported disappeared; can I assume the device mapper / dm-crypt is not a problem with regards to flushing?
Paul
Quoted 4 lines · Paul Schroeder
The btrfs wiki Main Page warns that "it is currently possible to corrupt a filesystem irrecoverably if your machine crashes or loses power on disks that don't handle flush requests correctly."
Quoted 9 lines
How do you know if this applies to your drives? Is there a way to test it, or a model list, or are newer SATA drives (magnetic, not SSDs) always ok? Does it depend on the controller? (I have a SiI 3114, latest BIOS.)
I would also be using btrfs on top of dm-crypt (with the latest release kernel). Some kernel versions ago, the message that write barriers aren't supported disappeared; can I assume the device mapper / dm-crypt is not a problem with regards to flushing?
Yeah if you don't see those messages you can be fairly certain you are ok. Thanks,
Josef
Excerpts from Josef Bacik's message of 2011-05-06 09:10:23 -0400:
Quoted 9 lines · Paul Schroeder
Quoted 8 lines
The btrfs wiki Main Page warns that "it is currently possible to corrupt a filesystem irrecoverably if your machine crashes or loses power on disks that don't handle flush requests correctly."
How do you know if this applies to your drives? Is there a way to test it, or a model list, or are newer SATA drives (magnetic, not SSDs) always ok? Does it depend on the controller? (I have a SiI 3114, latest BIOS.)
Quoted 8 lines
Quoted 5 lines
I would also be using btrfs on top of dm-crypt (with the latest release kernel). Some kernel versions ago, the message that write barriers aren't supported disappeared; can I assume the device mapper / dm-crypt is not a problem with regards to flushing?
Yeah if you don't see those messages you can be fairly certain you are ok. Thanks,
The easiest way to tell for sure is to do two tests:
dd if=/dev/zero of=/mnt/foo bs=4K count=10000 dd if=/dev/zero of=/mnt/foo bs=4K count=10000 oflag=sync
Run this with the filesystem mounted normally and again with the filesystem mounted -o nobarrier. -o nobarrier should be dramatically and hugely faster, almost like we're not writing to the disk at all.
-chris