Marcelo, the problem which I mentioned is with the limited number of write cycles in flash memory chips. The following document published in June 2007 by a USB flash drive vendor says the guaranteed number of write cycles for their USB flash drives is between 10.000 and 100.000:
http://www.corsairmemory.com/_faq/FAQ_flash_drive_wear_leveling.pdf Some vendors (including the one mentioned above) state that their drives use wear leveling so that write activity is distributed over a larger area to avoid that always the same cell will be overwritten again and again. Regards, Bernd Marcelo Leal wrote: >> Hi, > > Hello Bernd, > >> After I published a blog entry about installing >> OpenSolaris 2008.11 on a >> USB stick, I read a comment about a possible issue >> with wearing out >> blocks on the USB stick after some time because ZFS >> overwrites its >> uberblocks in place. > I did not understand well what you are trying to say with "wearing out > blocks", but in fact the uberblocks are not overwriten in place. The pattern > you did notice with the dtrace script, is the update of the uberblock that is > maintained in an array of 128 elements (1K each, just one active at time). > Each physical vdev has four labes (256K structures) L0, L1, L2, and L3. Two > in the begining and two at the end. > Because the labels are in fixed location on disk, is the only update that > zfs does not uses cow, but a two staged update. IIRC, the update is L0 and > L2,and after that L1 and L3. > Take a look: > > > http://cvs.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/fs/zfs/vdev_label.c > > So: > - The label is overwritten (in a two staged update); > - The uberblock is not overwritten, but do write to a new element on the > array. So, the transition from one uberblock(txg and timestamp) to another is > atomic. > > I'm deploying a USB solution too, so if you can clarify the problem, i would > appreciate it. > > ps.: I did look your blog, but did not see any comments around that, and the > comments section is closed. ;-) > > Leal > [http://www.eall.com.br/blog] > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
