<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman, new york, times, serif;font-size:12pt"><DIV>Thomas and James,</DIV>
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<DIV> Usually the partition is aligned to the Cylinder boundary. In the case of a LUN, the cylinder bondary might have no sense at all? Funny, I never tought about this before.</DIV>
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<DIV> There are some tools that can overwrite a few sectors on the start of the disk (lilo, grub, DOS fdisk), and expect the disk to have a partition table, where these sectors are not used for this reason. </DIV>
<DIV><BR> I don't know if OCFS2 has provisions for leaving this space unused.</DIV>
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<DIV>Regards,</DIV>
<DIV>Luis</DIV>
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<B><SPAN style="FONT-WEIGHT: bold">From:</SPAN></B> "Thomas.Zimolong@bmi.bund.de" <Thomas.Zimolong@bmi.bund.de><BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> james.masson@tradefair.com; ocfs2-users@oss.oracle.com<BR><B><SPAN style="FONT-WEIGHT: bold">Sent:</SPAN></B> Fri, July 9, 2010 11:24:38 AM<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> Re: [Ocfs2-users] partition offset/alignment on SAN devices.<BR></FONT><BR>> mkfs.ocfs2 -L SOMELABEL /dev/dm-10<BR>> This 64k (32/128k whatever) issue is usually only a problem if you've used<BR>a fdisk to create a<BR>> partition to put your data on. For hysterical reasons the first partition<BR>is created an arbitrary<BR>> amount of kb into the disk. This almost never lines up with the LUN<BR>raid-stripe. Then the I/O going<BR>> from app <> FS <> LUN <> disks overlaps block sizes - causing unnecessary<BR>I/O through the chain and<BR>> sub-optimal
performance.<BR><BR>Hi folks,<BR><BR>we had that issue too with our CX4-480 and the guys from EMC telling us not<BR>to forget the alignment.<BR><BR>So we first wondered how to automate this, because we'd have had to align the<BR>partitions on quite a few LUNs (more than 40).<BR>Since you'd have to use the expert options of fdisk, we did'nt find a quick<BR>solution with sfdisk, though with some further investigation there will<BR>surely be one.<BR><BR>But in the end this was not necessary anyway. We specifically requested that<BR>at EMC and they confirmed, that alignment is only a point when using<BR>partitions at all. We don’t use partitions, so no todo.<BR><BR>IMHO: Concerning the risk of destroying whatever is on the LUN: If someone<BR>thinks the LUN is unused, just because he/she sees no partition on it, isn't<BR>that more of "a lack of diligence"?<BR>We have a similar situation with ASM-devices: Even if you have a partition on<BR>it, it's not
mountable (as there's some ASM data inside it and no FS). So<BR>you'd always have to check more than that to be sure, that the device is<BR>unused.<BR><BR>Maybe you can clarify that with the vendor of your shared disks.<BR><BR>Greetings,<BR>Thomas<BR><BR>_______________________________________________<BR>Ocfs2-users mailing list<BR><A href="mailto:Ocfs2-users@oss.oracle.com" ymailto="mailto:Ocfs2-users@oss.oracle.com">Ocfs2-users@oss.oracle.com</A><BR>http://oss.oracle.com/mailman/listinfo/ocfs2-users<BR></DIV></DIV></div><br>
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