Roy, You want to use: pvcreate --dataalignment 128k /dev/sdXX This will guarantee that the start of the data area (pe_start) is aligned on a 128k boundary. Mike On Sat, Jul 11 2009 at 6:23am -0400, Roy Sigurd Karlsbakk <roy@karlsbakk.net> wrote: > Hi > > I came across an article on > http://thunk.org/tytso/blog/2009/02/20/aligning-filesystems-to-an-ssds-erase-block-size/ > about filesystem alignment. This mentions some issues about aligning > PVs in 128k bounderies. See snipped-out text from the article below. > > Are there flags like these or similar in helping admins using SSDs more > efficiently? > > roy > >> ... >> So I created a 1 gigabyte /boot partition as /dev/sdb1, and allocated >> the rest of the SSD for use by LVM as /dev/sdb2. And that’s where I ran >> into my next problem. LVM likes to allocate 192k for its header >> information, and 192k is not a multiple of 128k. So if you are creating >> file systems as logical volumes, and you want those volume to be >> properly aligned you have to tell LVM that it should reserve slightly >> more space for its meta-data, so that the physical extents that it >> allocates for its logical volumes are properly aligned. Unfortunately, >> the way this is done is slightly baroque: >> >> # pvcreate –metadatasize 250k /dev/sdb2 >> Physical volume “/dev/sdb2″ successfully created >> >> Why 250k and not 256k? I can’t tell you — sometimes the LVM tools >> aren’t terribly intuitive. However, you can test to make sure that >> physical extents start at the proper offset by using: >> >> # pvs /dev/sdb2 -o+pe_start >> PV VG Fmt Attr PSize PFree 1st PE >> /dev/sdb2 lvm2 – 73.52G 73.52G 256.00K >> >> If you use a metadata size of 256k, the first PE will be at 320k >> instead of 256k. There really ought to be an –pe-align option to >> pvcreate, which would be far more user-friendly, but, we have to work >> with the tools that we have. Maybe in the next version of the LVM >> support tools…. >> ... > -- > Roy Sigurd Karlsbakk > (+47) 97542685 > roy@karlsbakk.net > http://blogg.karlsbakk.net/ > -- > I all pedagogikk er det essensielt at pensum presenteres intelligibelt. > Det er et elementært imperativ for alle pedagoger å unngå eksessiv > anvendelse av idiomer med fremmed opprinnelse. I de fleste tilfeller > eksisterer adekvate og relevante synonymer på norsk. > > > _______________________________________________ > linux-lvm mailing list > linux-lvm@redhat.com > https://www.redhat.com/mailman/listinfo/linux-lvm > read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
