[lustre-discuss] llapi_file_get_stripe() and /proc/fs/lustre/osc restated

[John Bauer]

Robert

Excellent. It works like a champ, after changing llapi_get_name() to 
llapi_getname().

Thanks much.  If we meet up at a conference some day, I owe you dinner.

John


On 7/18/2016 6:13 PM, Read, Robert wrote:
> Hi John,
>
> The initial string in the OSC name is the filesystem name and the long 
> hexadecimal number at the end is the client ID. The client ID is 
> specific to the mount point that “owns” the OSC, and typically changes 
> each time the filesystem is mounted. It is there to differentiate 
> devices  when the same filesystem is mounted multiple times.
>
> You can retrieve both of the values by passing the mount directory to 
> llapi_get_name(). This function returns a string with filesystem name 
> and client ID in the format “FSNAME-ID". You can split the string on 
> the ‘-‘ to extract those values, and then use them construct the right 
> name for the current OSC being used for that file on that particular 
> mountpoint.
>
> Note, like the client ID, the OSC name is specific to that mount 
> point. The actual OST name is just FSNAME-OST####.
>
> robert
>
>> On Jul 18, 2016, at 15:22 , John Bauer <bauerj at iodoctors.com 
>> <mailto:bauerj at iodoctors.com>> wrote:
>>
>> I will restate the problem I am having with Lustre.
>>
>> With my I/O instrumentation library, I want to use 
>> *llapi_file_get_stripe*() to find the OSTs that a file of interest is 
>> striped on and then monitor only those OST's using files in the 
>> directory /proc/fs/lustre/osc.  This needs to be done 
>> programmatically, and in a general sense, with potentially only a 
>> relative path name.
>>
>> *llapi_file_get stripe*() yields
>> lmm_stripe_count:   1
>> lmm_stripe_size:    1048576
>> lmm_pattern:        1
>> lmm_layout_gen:     0
>> lmm_stripe_offset:  12
>>
>> lmm_oi.oi_fid *0x**194aa*
>>
>> *obdidx*           objid objid           group
>> *12* 31515860      0x1e0e4d4                0
>>
>> If I use *obdidx=12=0xc *to find the OST in directory 
>> /proc/fs/lustre/osc, I get multiple OSTs as there are multiple file 
>> systems with an ost of index 12 ( note that obdidx is decimal and 
>> entries in */proc/fs/lustre/osc* are hexadecimal, so we are looking 
>> for OST000c ).
>>
>> %ls -ld /proc/fs/lustre/osc/*OST000c*
>> dr-xr-xr-x 2 root root 0 Jul 18 14:31 
>> /proc/fs/lustre/osc/nbp1-OST000c-osc-ffff88090509f000
>> dr-xr-xr-x 2 root root 0 Jul 18 14:31 
>> /proc/fs/lustre/osc/nbp2-OST000c-osc-ffff881038061c00
>> dr-xr-xr-x 2 root root 0 Jul 18 14:31 
>> /proc/fs/lustre/osc/nbp6-OST000c-osc-ffff88084c405400
>> dr-xr-xr-x 2 root root 0 Jul 18 14:31 
>> /proc/fs/lustre/osc/nbp7-OST000c-osc-ffff8807a8e1d400
>> dr-xr-xr-x 2 root root 0 Jul 18 14:31 
>> /proc/fs/lustre/osc/nbp8-OST000c-osc-ffff88078339b800
>> dr-xr-xr-x 2 root root 0 Jul 18 14:31 
>> /proc/fs/lustre/osc/nbp9-OST000c-osc-ffff8807833a5400
>>
>> So I need to figure out which directory entry applies to the OST of 
>> my file of interest.
>>
>> I looked at the inode for clues.  I did an stat() of the file to get
>>
>> dev_t     st_dev=0xcc5d43c2
>> ino_t     st_ino=0x2000311ed0194aa
>>
>> I notice the *lov_user_md->oi_fid=0x0194aa,* populated by 
>> *llapi_file_get_stripe*(), is reflected in the lower part of *stat.st 
>> <http://stat.st>_ino=0x2000311ed0194aa*.  My question is, "Does the 
>> remainder of st_ino, *2000311ed*, give me any clue as to which OST I 
>> should use out of */proc/fs/lustre/osc*?"  The same question applies 
>> to the OST's objid=0x1e0e4d4and the file's st_dev=0xcc5d43c2.
>>
>> Because I know a priori that the file is in the lov nbp2, I know I 
>> need to find 
>> /proc/fs/lustre/osc/*nbp2-OST000c-osc-ffff881038061c00.***What does the
>> *ffff881038061c00 *represent?It is the same value for all OST's in a 
>> given lov, so I am guessing it is lov related.*
>> *
>>
>> There are over 1200 OST on the node, so I want to minimize the number 
>> that I instrument.
>> Any information that would shed some light on this would be greatly 
>> appreciated.
>> John
>> -- 
>> I/O Doctors, LLC
>> 507-766-0378
>> bauerj at iodoctors.com
>> _______________________________________________
>> lustre-discuss mailing list
>> lustre-discuss at lists.lustre.org <mailto:lustre-discuss at lists.lustre.org>
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>

-- 
I/O Doctors, LLC
507-766-0378
bauerj at iodoctors.com

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