Hi, Andreas
The lfs-setstripe man page for option '-C' indicates only negative values
can be used, and the file will be striped over all available OSTs. However,
my wish is to stripe a file over only a subset set of available OSTs.
Is it possible to achieve that?
I just now tried the two commands below without '-o' option. My intent
is to create a file with stripe count of 8 over 4 OSTs. But they both
ended up with the same result of no overstriping.
% lfs setstripe -c 4 -C 8 $SCRATCH/dummy
% lfs setstripe -C 8 $SCRATCH/dummy
% lfs getstripe $SCRATCH/dummy
/pscratch/sd/w/wkliao/dummy
lmm_stripe_count: 8
lmm_stripe_size: 1048576
lmm_pattern: raid0
lmm_layout_gen: 0
lmm_stripe_offset: 168
lmm_pool: original
obdidx objid objid group
168 19587711 0x12ae27f 0x368000041f
169 19224808 0x12558e8 0x36c0000428
170 19783691 0x12de00b 0x3700000413
171 20429006 0x137b8ce 0x3740000419
172 19633677 0x12b960d 0x3780000421
173 20027491 0x1319863 0x37c0000402
174 19912786 0x12fd852 0x3800000401
175 20862151 0x13e54c7 0x3840000418
As for using llapi_layout APIs, I am doing the followings. It seems like
I miss some API call to set the number of overstipes or number of stripes
per OST, as they would not achieve an overstriping setting.
struct llapi_layout *layout = llapi_layout_alloc();
err = llapi_layout_pattern_set(layout, LLAPI_LAYOUT_OVERSTRIPING);
err = llapi_layout_stripe_count_set(layout, 8);
fd = llapi_layout_file_create(path, O_CREAT|O_RDWR, 0660, layout);
I found the only way to achieve overstriping is to call
err = llapi_layout_ost_index_set(layout, stripe_number, ost_index);
However, I must pick the values for argument 'ost_index'.
Wei-keng
> On Dec 22, 2025, at 4:32 AM, Andreas Dilger <[email protected]>
> wrote:
>
> You should be able to use "-C N" to overstripe a file without specifying the
> OST indexes with "-o ...".
>
> For handling this via llapi_layout commands, I believe it is necessary to set
> llapi_layout_pattern_set(LLAPI_LAYOUT_OVERSTRIPING) flag on the component,
> and then specify a stripe count > OSTCOUNT. I see this isn't documented in
> the llapi_layout_pattern_set(3) man page (along with LLAPI_LAYOUT_FOREIGN),
> so please file a Jira ticket for this (and ideally also submit a patch to the
> man page).
>
> The flag will be cleared if the stripe count <= OSTCOUNT, for improved
> compatibility with older clients that do not understand overstriping (though
> that is unlikely these days).
>
> The patch
> https://urldefense.com/v3/__https://review.whamcloud.com/54192__;!!Dq0X2DkFhyF93HkjWTBQKhk!WfAgqXmWvikjup5ElLwLsZJgoZKUnWW5SoI78awomasNdwbkf6Z93WQJk7s3RlYK7WjKpirPXZDYqPxEnZKilN5g5Wpb5IY$
> ("LU-16938 utils: setstripe overstripe multiple OST count") along with a
> few follow-on fixes in Lustre 2.16+ also allows specifying:
>
> lfs setstripe -C -N ... FILE|DIR
>
> (or llapi equivalent) to create 'N' stripes per OST for the file, instead of
> having to know the exact OST count, if that is more convenient.
>
> Cheers, Andreas
>
>> On Dec 20, 2025, at 18:52, Wei-Keng Liao via lustre-discuss
>> <[email protected]> wrote:
>>
>> When setting the overstriping for a new file, is it possible to let
>> the MDS to choose the OST indices?
>>
>> I was able to use lfs command to set an overstiping for a new file.
>> For example, to overstripe a file over 4 OSTs with 2 stripe per OST,
>> I am using this command:
>>
>> % lfs setstripe -c 4 -C 8 -o 10-13,10-13 $SCRATCH/dummy
>>
>> % lfs getstripe $SCRATCH/dummy | grep lmm
>> lmm_stripe_count: 8
>> lmm_stripe_size: 1048576
>> lmm_pattern: raid0,overstriped
>> lmm_layout_gen: 0
>> lmm_stripe_offset: 10
>> lmm_pool: original
>>
>> My understanding is when without overstriping, the default is that
>> the OSTs are selected by Lustre MDS based on some policy (maybe OST
>> usage). I wonder if this can also apply to overstriping, i.e. using
>> lfs command options '-c' and '-C' without option '-o'.
>>
>> I am also wondering how this can be achieved using the Lustre user
>> C APIs, when making calls to llapi_layout_ost_index_set().
>>
>>
>> Wei-keng
>>
>> _______________________________________________
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>> https://urldefense.com/v3/__http://lists.lustre.org/listinfo.cgi/lustre-discuss-lustre.org__;!!Dq0X2DkFhyF93HkjWTBQKhk!WfAgqXmWvikjup5ElLwLsZJgoZKUnWW5SoI78awomasNdwbkf6Z93WQJk7s3RlYK7WjKpirPXZDYqPxEnZKilN5gQzWGvgU$
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