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QNX 6 file system file size limit

Discussion about the QNX6 OS.

QNX 6 file system file size limit

Postby hello » Thu Feb 07, 2013 3:56 am

Hi,
QNX 4 file systems has a file size limit of 2GB. Could you please tell the file size limit in QNX 6 file system

Regards,
hello
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Re: QNX 6 file system file size limit

Postby space » Fri Aug 30, 2013 5:59 pm

According to the documentation here: http://www.qnx.com/developers/docs/6.5.0_sp1/index.jsp?topic=%2Fcom.qnx.doc.neutrino_user_guide%2Flimits.html&resultof=%22limits%22%20%22limit%22%20&anchor=QNX6_limits qnx6_fs is limited to 256GB.
I believe Qnx6_fs is not available before QNX 6.5.
All versions of QNX 6 use the qnx4_fs by default.
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Re: QNX 6 file system file size limit

Postby maschoen » Sat Aug 31, 2013 12:21 am

As I read that documentation, it was saying that with a 1KB (default) block size, with three levels of indirect pointers you can have a 256GB file. Nowhere did it say that 3 levels was the maximum. So it's possible that the limitation is the 64-bit addressing, which would mean that a file can be as large as a hard drive for the foreseeable future.
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Re: QNX 6 file system file size limit

Postby Thunderblade » Mon Sep 02, 2013 7:33 am

space wrote:All versions of QNX 6 use the qnx4_fs by default.

Not sure what you mean - it depends on what is specified in the build file, and I've seen several BSPs which use fs-qnx6, or offer both. For CD-based installations to HDD/SSD, it offers "Type 179" first, which is a fs-qnx6 partition type.

As fs-qnx6 is a Copy-On-Write system, I'd use it only on real hard disks. Flash based media do too much "on their own" that the filesystem isn't aware of, plus the Copy-On-Write contributes to the wearout of the device.
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Re: QNX 6 file system file size limit

Postby maschoen » Mon Sep 02, 2013 8:21 am

Thunderblade wrote:As fs-qnx6 is a Copy-On-Write system, I'd use it only on real hard disks. Flash based media do too much "on their own" that the filesystem isn't aware of, plus the Copy-On-Write contributes to the wearout of the device.


I'm curious about what this Copy-On-Write means. Surely it doesn't mean that if I have a 1Gig file and I seek to the center, write a block that the file system copies the entire 1Gig file and then changes the pointer? I'm pretty sure that if you open an existing file for write and write new data that regardless what happens, power cycle or whatever, anytime during the process that when you reboot you will either get the original file intact or the new file. I also am pretty sure that you can't get an inconsistent file system the way you can with fs-qnx4 if the power fails at the wrong time.
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