On Wed, Mar 29, 2000 at 09:08:32AM +0200, Marc SCHAEFER wrote:
> Scott Henry <scotth@sgi.com> wrote:
> > You are thinking of the other type, a log-based filesystem, where
> > metadata and user data are logged. It is much more difficult to
>
> Maybe I am mixing up oranges and logs, but for me, in certain cases,
> a log-based filesystem can be way faster than a normal or
> metadata-log filesystem: as data is only appended, you can do
> the append sequentially and in very big chunks (say, 4 MBytes
> sequential I/Os). You will get very good performance from
> single device and hardware (or even software) RAID0. And
> you don't need to think about seek times when writing.
>
> Of course, in theory this also means you have to add a new disk
> drive every now and then, unless some data reclaimation is
> done. Which brings in new problems.
>
> This can of log file system (with data reclaimation) ressembles
> a bit the HSM system when using tapes for data migration.
The way this is done on Tandem NonStop systems requires cooperation
of the applications:
1. Files/tables that need to be logged are marked with an AUDIT flag.
2. Applications define complete transactions by means of calls like
BEGINTRANSACTION, ENDTRANSACTION, ABORTTRANSACTION.
When a process fails, active transaction(s) associated with that
process are rolled back automatically by the Transaction Monitoring
Facility.
3. The transactions are logged sequentially to socalled 'audittrails'
on separate disks.
4. Regularly 'online dumps' are made of the audited tables.
File recovery is possible by restoring from the online dump and
replaying the audittrails. The consistency of the database is
garanteed.
5. Audittrails are backed up to cheaper media and subsequently released,
once they do not contain active transactions any longer.
6. Online dumps and backed up audittrails are automatically released,
once they are no longer needed for file/volume recovery.
(i.e. there are newer online dumps available)
On Tandem you'll get much better performance _with_ auditing (logging)
transactions than without.
Toon.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Fri Mar 31 2000 - 21:00:24 EST