On 05/12/13 18:46, Charles Manning wrote:
> On Friday 06 December 2013 01:27:09 Dominic Raferd wrote:
>>   I am responsible for a PBX system which uses embedded uClinux on 256MB
>> internal memory disk, this uses YAFFS2 filesystem and it is rapidly running
>> out of memory. df used space is 240MB (96% of total) and du used space is
>> 76MB. Once df gets to 100% used I guess the whole system will fail and be
>> irrecoverable. I don't understand much about YAFFS but here is some info:
>>
>>   root@G-124:~# cat /proc/yaffs
>>   YAFFS built:Apr 22 2010 11:02:12
>>   $Id: yaffs_fs.c,v 1.89 2009-11-29 21:50:10 charles Exp $
>>   $Id: yaffs_guts.c,v 1.98 2009-12-07 01:17:33 charles Exp $
>>
>>
>>   Device 0 "file system"
>>   startBlock......... 0
>>   endBlock........... 1951
>>   totalBytesPerChunk. 2048
>>   nDataBytesPerChunk. 2048
>>   chunkGroupBits..... 0
>>   chunkGroupSize..... 1
>>   nErasedBlocks...... 63
>>   nReservedBlocks.... 5
>>   blocksInCheckpoint. 0
>>   nTnodesCreated..... 97500
>>   nFreeTnodes........ 41
>>   nObjectsCreated.... 96700
>>   nFreeObjects....... 92
>>   nFreeChunks........ 8822
>>   nPageWrites........ 8033
>>   nPageReads......... 89169
>>   nBlockErasures..... 180
>>   nGCCopies.......... 4471
>>   garbageCollections. 72
>>   passiveGCs......... 0
>>   nRetriedWrites..... 0
>>   nShortOpCaches..... 10
>>   nRetireBlocks...... 0
>>   eccFixed........... 0
>>   eccUnfixed......... 0
>>   tagsEccFixed....... 0
>>   tagsEccUnfixed..... 0
>>   cacheHits.......... 20
>>   nDeletedFiles...... 0
>>   nUnlinkedFiles..... 56
>>   nBackgroudDeletions 0
>>   useNANDECC......... 1
>>   noTagsECC.......... 0
>>   isYaffs2........... 1
>>   inbandTags......... 0
>>   emptyLostAndFound.. 0
>>   disableLazyLoad.... 0
>>
>>   (The mounting memory loss may be related to frequent power cuts. Is there
>> anything that can be done to recover the lost memory (currently 164MB)
>> before the system fails entirely?
>>
>>   I would be very grateful for some urgent help/input, and can pay something
>> for a positive resolution. (The PBX box also has an attached USB drive
>> (8GB) but although this is working fine I don't believe the system can boot
>> from here, and it has no local interface, only via ethernet.)
> Hello Dominic
>
> If you have a wide disparity between du and df this typically means that you
> have lots of small files.
>
> du just adds up file contents and such to estimate space used with no
> knowledge of file system layout. It makes various guesses. df asks the file
> system what space is in use so that is a more accurate value.
>
> If you store a 1-byte file in Yaffs you will end up with:
> 1x object header chunk + 1x data chunk = 2 chunks = 4k on your system.
>
> However that overhead is fixed, so if you have a 1MB file, it just takes up
> 1MB + 1x object header chunk = 1MB + 2048 bytes.
>
> So... what are you storing that you can get rid of?
>
>

Thanks for the response Charles. But there are very few small files in 
this system. If I mount this boot device at /tmp/mnt/mtdblock1:
# find /tmp/mnt/mtdblock1 -size -10c|wc -l
87
# find /tmp/mnt/mtdblock1 -size -100c|wc -l
281