Re: Mixed and raid [was Re: BUG: btrfsRe: Does btrfs "raid1" actually provide any resilience?]

[Anand Jain <Anand.Jain@oracle.com>]

Hi G.Baroncelli, Lutz,

  Thanks for the test case and heads-up on this. The code missed
  the check if the user has provided the option before default
  profile for the mixed group (due to small vol) is enforced.

  I have sent out the following patch to fix it.

[PATCH] btrfs-progs: for mixed group check opt before default raid 
profile is enforced

  Kindly let us know how it performed if you could.

  Thanks,
Anand


On 11/15/2013 05:21 AM, Goffredo Baroncelli wrote:
> Hi Anand,
>
> after some tests and looking at the code I discovered that the current
> mkfs.btrfs doesn't allow any raid profile other than SINGLE for data and
> meta-data when the mixed metadata/data group is enabled. It seems this
> behaviour was introduce by a your commit [1].
>
>
> mkfs.c line 1384 onwards
>
> 	/*
> 	* Set default profiles according to number of added devices.
> 	* For mixed groups defaults are single/single.
> 	*/
> 	if (!mixed) {
> [....]
> 	} else {
> 		u32 best_leafsize = max_t(u32, sysconf(_SC_PAGESIZE),
> 				sectorsize);
> 		metadata_profile = 0;
> 		data_profile = 0;
>
>
> But in another your commit [2] it seems that you check that in case of
> mixed, the metadata and data profile have to be equal (implicitly
> allowing that they could be different than single ?).
>
> mkfs.c line 1373 onward
>
> 	if (is_vol_small(file)) {
> 		printf("SMALL VOLUME: forcing mixed metadata/data
> 				groups\n");
> 		mixed = 1;
> 		if (metadata_profile != data_profile) {
> 			if (metadata_profile_opt || data_profile_opt) {
> 				fprintf(stderr, "With mixed block
> 	 groups data and metadata profiles must be the same\n");
> 				exit(1);
> 			}
> 		}
> 	}
>
>
> So I am a bit confusing: it is allowed a raid profile different than
> single when the mixed is enabled ? Of course mixed and raid together
> doesn't make sense (or almost make very little sense) but the code of
> mkfs is a bit confused, and a warning should be raised when the raid
> profile are forced to a default different from the one selected by the user.
>
>
> Thanks for the attention.
> BR
> G.Baroncelli
>
>
> [1] btrfs-progs: avoid write to the disk before sure to create fs
> 71d6bd3c8d70fb682c7fd50796f587ce1f1cf6f8
> .
> [2] btrfs-progs: mkfs should check for small vol well before
> cdbc10729266c03aeb2eb812c17a3ef6c1ceae26
>