Hi Andi,
On Thu, 15 Feb 2007, Andi Kleen wrote:
Juan Piernas Canovas <[email protected]> writes:
[playing devil's advocate here]
If the data and meta-data devices of DualFS can be on different disks,
DualFS is able to READ and WRITE data and meta-data blocks in
PARALLEL.
XFS can do this too using its real time volumes (which don't contain
any metadata). It can also have a separate log.
But you still need several 'real' devices to separate data and meta-data
blocks. DualFS does the same with just one real device. Probably 'data
device' and 'meta-data device' names are a bit confusing. Think about
them as partitions, not as real devices.
Also many storage subsystems have some internal parallelism
in writing (e.g. a RAID can write on different disks in parallel for
a single partition) so i'm not sure your distinction is that useful.
But we are talking about a different case. What I have said is that if you
use two devices, one for the 'regular' file system and another one for the
log, DualFS is better in that case because it can use the log for reads.
Other journaling file systems can not do that.
If you stripe two disks with a standard fs versus use one of them
as metadata volume and the other as data volume with dualfs i would
expect the striped variant usually be faster because it will give
parallelism not only to data versus metadata, but also to all data
versus other data.
If you have a RAID system, both the data and meta-data devices of DualFS
can be stripped, and you get the same result. No problem for DualFS :)
Also I would expect your design to be slow for metadata read intensive
workloads. E.g. have you tried to boot a root partition with dual fs?
That's a very important IO benchmark for desktop Linux systems.
I do not think so. The performance of DualFS is superb in meta-data read
intensive workloads. And it is also better than the performance of other
file system when reading a directory tree with several copies of the Linux
kernel source code (I showed those results on Tuesday at the LSF07
workshop).
-Andi
Regards,
Juan.
--
D. Juan Piernas Cánovas
Departamento de Ingeniería y Tecnología de Computadores
Facultad de Informática. Universidad de Murcia
Campus de Espinardo - 30080 Murcia (SPAIN)
Tel.: +34968367657 Fax: +34968364151
email: [email protected]
PGP public key:
http://pgp.rediris.es:11371/pks/lookup?search=piernas%40ditec.um.es&op=index
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