From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <51E916A8.1000101@redhat.com> Date: Fri, 19 Jul 2013 12:36:24 +0200 From: Zdenek Kabelac MIME-Version: 1.0 References: <1374172980.23440.10.camel@heisenberg.scientia.net> In-Reply-To: <1374172980.23440.10.camel@heisenberg.scientia.net> Content-Transfer-Encoding: quoted-printable Subject: Re: [linux-lvm] some questions Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="iso-8859-1"; format="flowed" To: LVM general discussion and development Cc: Christoph Anton Mitterer Dne 18.7.2013 20:43, Christoph Anton Mitterer napsal(a): > Hi. > > I'd have some questions... > > 1) Is the --discards option the same than the issue_discards option from > the config file? Since the one defaults to 0 the other to passdown? > If not what's the difference? Nope --discards options is for thin volume in thin pool - while lvm.conf option = is=20 about discarding free space in VG - in general - unless you are using some virtual storage for PVs - it's not a wise idea to enable issue_discards, since it makes recovery (i.e. going one step back) impossible - what is=20 discarded cannot be recovered... For thin volumes - it could be used to free already provisioned space from = pool (as well as getting native discard on SSD if the pool is on SSD). Behaviour is configurable. > 2) Of an existing LV, can I see how data was actually allocated? And how > can I see the alloc policy of a VG? vgdisplay doesn't show it. Looks like this attribute should be added to lvs/vgs. For now only lvdisplay shows allocation policy for LV. To see allocated extents you could use: lvs -o+seg_pe_ranges > 3) Do I see that correctly, when I use Normal as alloc policy,... it > will try to do contiguous allocation... and only do not so,... if not > possible? Yes > 4) md_component_detection and md_chunk_alignment > Will these also work if there is another block layer (e.g. dmcrypt) in > between? Especially the md_chunk_alignment? it's only one-layer check - there is no device stack analysis. > 5) What alignments are needed? > "md_chunk_alignment =EF=BF=BD If set to 1, and a Physical Volume is placed > directly upon an md device, LVM2 will align its data blocks with the md > device's stripe-width." What is visible in sysfs is used. It's responsibility of each device to provide correct values for alignment. i.e. if you have crypted mdraid device - then crypto needs to export right values. Zdenek