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file system, separating meta-data and data, DualFS/GPFS
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wildhorse
Tux's lil' helper
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Joined: 16 Mar 2006
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Location: Estados Unidos De América

PostPosted: Sun Apr 19, 2009 7:57 am    Post subject: file system, separating meta-data and data, DualFS/GPFS Reply with quote

Most file systems store the meta-data (allocation table, directories etc.) and the data (the files' contents) on the same disk. That is fine if you have only one disk. But I have lots of disks and I like to address them as one huge file system. Every tíme I access the file system, most disks are being accessed because the meta-data are spread over the disks.

Heat is a problem if you have too many disks. Trust me, disks die because of too much heat. :oops: That is why I put disks into idle mode. The disks are also distributed over multiple computers, which I would like to put into idle mode, too. The whole idea of minimizing the number of disks in online mode at any time does not work in practice with common file systems, because even for a simple directory listing most disks have to be accessed.

Separating the meta-data and data also allows me to backup the information differently. Most of the data can be recovered from tape, but a problem with the meta-data may kill the entire (Huge!) file system. With LVM2 and something like DualFS (see below), I can use RAID1 or RAID5 for the meta-data and RAID0 (no backup) for the data. :idea:

So far I found two possible solutions, namely DualFS and IBM General Parallel File System (GPFS). DualFS (http://ditec.um.es/~piernas/dualfs/) from Spain is very promising, but the authors warn that the software is in an experimental state with bugs. GPFS seems to be close-source and a bit overkill.

Do you know any Linux file system, hopefully with Gentoo support, which does implement the idea of separating meta-data and data over different disks?
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pigeon768
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Joined: 02 Jan 2006
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PostPosted: Mon Apr 20, 2009 8:42 pm    Post subject: Reply with quote

OCFS2 and GFS2 are in the kernel, and are both cluster fs', which may give what you're asking for.

As for heat: add more fans.
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wildhorse
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Joined: 16 Mar 2006
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Location: Estados Unidos De América

PostPosted: Sun Apr 26, 2009 9:04 am    Post subject: Reply with quote

I checked the documentation of GFS and OCFS2. GFS and OCFS2 are optimized for parallel access with high performance in mind. Neither GFS nor OCFS2 allow us to store the meta-data and data on separate disks. Both file systems spread the meta-data with the data over all disks.

Red Hat's GFS is obsolete. I encountered plenty of dead links on the GFS web pages.
GFS2 is in development state. I could not find any indication that GFS2 separates meda-data and data. Besides, I need a stable file system.

Oracle's OCFS2 is stable, but it does not come with the feature I want. OCFS2 also depends on JBD, which currently limits the size of the file system to 16 TB. That is too small for me. JBD2 should address that issue in the future.

Anyway, thanks for the suggestions, but I still have no alternative, stable file system that allows me to store the meta-data on one disk (or more) and the data on additional disks completely separated from the meta-data.

Anybody with another suggestion?

About the fans: my machines already have 5 fans each, with 2 fans located infront of the disks, not counting internal fans like the CPU fan. But when your system reaches a certain size, there is very little you gain from fans. Try to cool your house with a fan in the summer. You need a different strategy. Reducing the heat load at the source is the cheapest solution.
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Mr. Tao
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Joined: 20 Jul 2007
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PostPosted: Sun Apr 26, 2009 11:31 pm    Post subject: Reply with quote

Have you considered Lustre?
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