Josh-D. S. Davis

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HOWTO: AIX support for R/W filesystem on USBMS
Josh 2014
joshdavis
Putting JFS2 on non-LVM block devices has been working for a long time. I​ wrote up how to put JFS2 on a ramdisk back at AIX 4.3.3. I lost the techdoc from back then, but IBM has a newer re-write dated 2008 here: http://www-01.ibm.com/support/docview.wss?uid=isg3T1010722

JFS2 requires the

Putting JFS2 on non-LVM block devices has been working for a long time. I​ wrote up how to put JFS2 on a ramdisk back at AIX 4.3.3. I lost the techdoc from back then, but IBM has a newer re-write dated 2008 here: http://www-01.ibm.com/support/docview.wss?uid=isg3T1010722

JFS2 requires the underlying system to tell it if something goes away, or for it to stay there as long as the filesystem is mounted. LVM does this for disk, and the ramdisk drivers do this as well (mostly because if the ramdisk fails, likely the system has failed). The key there is that with JFS2, the ramdisk pages are pinned.

I wrote up including performance on USB 1 and USB2 ports in January of 2010 HOWTO: JFS2 on USB device on AIX 5.3.11.1. Everything is fine, and dandy, even mount on boot, except it's not supported by AIX Development.

The problem for USB Mass Storage Devices is that the device can just go away unexpectedly. If a disk goes into deep sleep, or resets because of a loose connection, the JFS drivers do not get notified. So, they take writes, and JFS2 saves them up until it's time to flush. It goes to flush, and the I/O channel is gone. Sometimes, this is just loss of everything in cache. If it's an important file, then the system crashes.

​Because of that, we still cannot put LVM on a USB Mass Storage Device. This would take changes to notification of device availability, perhaps changes to the sync daemon, etc. Who knows, but there's not been enough push from paying customers to make it a priority for AIX Development. Until that happens, don't expect formal support for JFS2 on these devices.

ALL IS NOT LOST!

AIX development supports read/write and even booting from USB Mass Storage Devices, but only with UDFS. The purpose is for writing a mksysb (system boot) image, or tar/cpio files, etc, and exists because of the RDX USB Internal Dock sold with some systems. https://www.ibm.com/support/knowledgecenter/en/ssw_aix_61/com.ibm.aix.files/usbms_fileref.htm

​Boot support is provided as well: REF: ​http://www-01.ibm.com/support/docview.wss?uid=isg1IZ66737

More info on RDX USB Internal Dock. https://www.ibm.com/support/knowledgecenter/POWER7/p7hdt/fc1103.htm

However, RDX is just a hot-swap USB to SATA drive bay. Any current USB drive (USB3 is preferred due to performance), should work fine.

Bootable filesystem
mksysb -eXpi /dev/usbms0

Normal filesystem
udfcreate -d /dev/usbms0

Access read/write
mount -vudfs /dev/usbms0 /USBDRIVE


http://omnitech.net/reference/2017/08/02/howto-aix-support-for-rw-filesystem-on-usbms/

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