| Title: | AdvFS Support/Info/Questions Notefile |
| Notice: | note 187 is Freq Asked Questions;note 7 is support policy |
| Moderator: | DECWET::DADDAMIO |
| Created: | Wed Jun 02 1993 |
| Last Modified: | Fri Jun 06 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 1077 |
| Total number of notes: | 4417 |
Hello,
I've made a 10Mb adfvs domain/fileset and created a lot of small (less then 500
byte) in it until the disk was full.
Begin situation just after the domain/fileset creation:
# df -ki .
Filesystem 1024-blocks Used Avail Capacity Iused Ifree %Iused Moun
ted on
test_domain#test 10000 16 5744 0% 2 19621 0% /mnt
Situation after the file creation:
# df -ki .
Filesystem 1024-blocks Used Avail Capacity Iused Ifree %Iused Moun
ted on
test_domain#test 10000 3685 0 100% 3461 3763 48% /mnt
When I remove the file not all space is reclaimed
Situation after removing all files:
# df -ki .
Filesystem 1024-blocks Used Avail Capacity Iused Ifree %Iused Moun
ted on
test_domain#test 10000 16 240 6% 2 8039 0% /mnt
As you can see of the 5744k I had originaly free only 240k remains after
this create/delete action. As far as I understand advfs most of the space is
held in the fragment file (.tags/1) and in the bitmap file (.tags/M-6).
Now the strangness comes. At this point I can create all the small files
again without any problems (+/- 3600k). But I can't create a file which is
bigger than the available space (240k).
The only explanation I can give is that not only blocks in the bitmap file
cannot be reused bot also the blocks in the fragment file when the request
is for more than 8k. This also implies that if you initialy make a lot
of small files and removed them afterwards you loose this space forever for
bigger files.
I'm I wrong
/Peter
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 1034.1 | You are right. | NETRIX::"[email protected]" | jwang | Mon Apr 07 1997 14:40 | 5 |
Yes. This is a known problem for AdvFS. As you mentioned, creating a lot of small files renders in fragmenting the BMT (bitfile metadata table) and not leaving room for user data. Development effort are given to address this problem in future releases. [Posted by WWW Notes gateway] | |||||
| 1034.2 | UTRTSC::WINDMEIJER | Tue Apr 08 1997 03:24 | 44 | ||
If I understand you correctly then the fragmentation if the BMT will
makes it impossible to reuse the data in the fragment file.
What I did is making a file domain with the -p option so the BMT will
be preallocated. (almost no fragmentation)
mkfdmn -o -p 220 /dev/rz3a test_domain
showfile -x M-6 give 9 fragments. The size of .tags/1 and .tags/M-6
were
# ls -l 1 M-6
---------- 0 root system 3538944 Jan 1 1970 1
---------- 0 root system 2080768 Jan 1 1970 M-6
# df -ik /mnt
Filesystem 1024-blocks Used Avail Capacity Iused
Ifree %Iused Mounted on
test_domain#test 10000 3717 0 100% 3465
3647 49% /mnt
After the removal of the files:
# ls -l 1 M-6
---------- 0 root system 3538944 Jan 1 1970 1
---------- 0 root system 2080768 Jan 1 1970 M-6
# df -ik /mnt
Filesystem 1024-blocks Used Avail Capacity Iused
Ifree %Iused Mounted on
test_domain#test 10000 16 272 6% 2
8036 0% /mnt
As you can see I still have only 272 blocks available. Why can't I
reuse the free block in the fragment file. (.tags/1)
/Peter
[End of buffer]
| |||||
| 1034.3 | Threshold for freeing space in frag file | NETRIX::"[email protected]" | jwang | Tue Apr 08 1997 13:00 | 11 |
AdvFS only free up space held in the fragment file when a configurable threshold is exceeded. The size of the fragment file in your example has not exceeded the default threshold which is set for larger domains. The threshold is for the whole system and one needs to be careful about changing it. You can see that small domain is not too meaningful due to % usage by the AdvFS overhead: the log, the BMT, the fragment file, as shown by your df -ik right after you create the domain and after you removes those small files. If you really need to create small domains, the threshold can be tuned to smaller number to allow reusing space previously allocated to the fragment file for large files. [Posted by WWW Notes gateway] | |||||