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 -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: How to know whether disks handle flush requests correctly
On 05/06/2011 05:13 AM, Paul Schroeder wrote: 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? Yeah if you don't see those messages you can be fairly certain you are ok. Thanks, Josef -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: How to know whether disks handle flush requests correctly
Excerpts from Josef Bacik's message of 2011-05-06 09:10:23 -0400: On 05/06/2011 05:13 AM, Paul Schroeder wrote: 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? 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=1 dd if=/dev/zero of=/mnt/foo bs=4K count=1 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 -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
