From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx3.redhat.com (mx3.redhat.com [172.16.48.32]) by int-mx1.corp.redhat.com (8.11.6/8.11.6) with ESMTP id k0L1tD120716 for ; Fri, 20 Jan 2006 20:55:13 -0500 Received: from mail.packetmotion.com (66-147-215-243.focaldata.net [66.147.215.243] (may be forged)) by mx3.redhat.com (8.13.1/8.13.1) with ESMTP id k0L1t1XL032266 for ; Fri, 20 Jan 2006 20:55:06 -0500 Received: from pmi00exf00.us.packetmotion.com (unknown [66.147.215.243]) by mail.packetmotion.com (Postfix) with ESMTP id 5A4D1E0082 for ; Fri, 20 Jan 2006 17:53:54 -0800 (PST) Content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01C61E2D.939CF3DB" Date: Fri, 20 Jan 2006 17:54:12 -0800 Message-ID: From: "Alex Chen" Subject: [linux-lvm] Difference in LVM and LVM2 and their strength/weakness 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: To: linux-lvm@redhat.com This is a multi-part message in MIME format. ------_=_NextPart_001_01C61E2D.939CF3DB Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Greetings, I am tasked to investigate the differences between LVM and LVM2. I am new to LVM so it would be greatly appreciated if someone can explain or point me to the right direction for the following questions: =20 1. What does LVM2 have that is not available in LVM? Or is it a only better architectured implementation of LVM? 2. Which version of Red Hat enterprise system uses which LVM? And does the user need to do any configuration during installation? 3. If LVM2 is definitely better than LVM, how stable is it? =20 Thanks. Alex ------_=_NextPart_001_01C61E2D.939CF3DB Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Greetings,

  I am tasked to investigate the differences = between LVM and LVM2.  I am new to LVM so it would be greatly appreciated = if someone can explain or point me to the right direction for the following = questions:

 

  1. What does LVM2 have = that is not available in LVM?  Or is it a only better architectured = implementation of LVM?
  2. Which version of Red = Hat enterprise system uses which LVM?  And does the user need to = do any configuration during installation?
  3. If LVM2 is definitely = better than LVM, how stable is it?

 

Thanks.

Alex

------_=_NextPart_001_01C61E2D.939CF3DB-- From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from o.ww.redhat.com (vpn-4-1.stuttgart.redhat.com [10.32.4.1]) by pobox.stuttgart.redhat.com (8.12.8/8.12.8) with ESMTP id k0LH8K4W010128 for ; Sat, 21 Jan 2006 18:08:20 +0100 Date: Sat, 21 Jan 2006 18:08:20 +0100 From: Heinz Mauelshagen Subject: Re: [linux-lvm] Difference in LVM and LVM2 and their strength/weakness Message-ID: <20060121170820.GA2797@redhat.com> References: Mime-Version: 1.0 Content-Disposition: inline In-Reply-To: Reply-To: mauelshagen@redhat.com, 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="us-ascii" Content-Transfer-Encoding: 7bit To: LVM general discussion and development On Fri, Jan 20, 2006 at 05:54:12PM -0800, Alex Chen wrote: > Greetings, Hi. > > I am tasked to investigate the differences between LVM and LVM2. I am > new to LVM so it would be greatly appreciated if someone can explain or > point me to the right direction for the following questions: > > > > 1. What does LVM2 have that is not available in LVM? It has command line extensions beyond lvm (eg, vgs, lvs, pvs commands). It's configurable in various regards (eg, device name filters) The limits of 256 grand total logical volumes and ~64k extents per logical volume are gone. Logical volume snapshots are asynchronous rather than synchronuous and gain better performance. pvmove (online data relocation) is based on temporary, restartable mirrors which wasn't the case in LVM1. > Or is it a > only better architectured implementation of LVM? I'ld not say 'only', but yes, it is :) > 2. Which version of Red Hat enterprise system uses which LVM? And > does the user need to do any configuration during installation? RHEL3 comes with LVM, RHEL4 with LVM2. > 3. If LVM2 is definitely better than LVM, how stable is it? It is stable with the exception of rare snapshot issues, we're fixing right now. > > > > Thanks. > > Alex > > _______________________________________________ > 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/ -- Regards, Heinz -- The LVM Guy -- *** Software bugs are stupid. Nevertheless it needs not so stupid people to solve them *** =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Heinz Mauelshagen Red Hat GmbH Consulting Development Engineer Am Sonnenhang 11 Cluster and Storage Development 56242 Marienrachdorf Germany Mauelshagen@RedHat.com +49 2626 141200 FAX 924446 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- From mboxrd@z Thu Jan 1 00:00:00 1970 Content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="----_=_NextPart_001_01C61FC3.07ABF28F" Subject: RE: [linux-lvm] Difference in LVM and LVM2 and their strength/weakness Date: Sun, 22 Jan 2006 18:16:33 -0800 Message-ID: From: "Alex Chen" 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: To: mauelshagen@redhat.com, LVM general discussion and development This is a multi-part message in MIME format. ------_=_NextPart_001_01C61FC3.07ABF28F Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Heinz, thanks for the information/ =20 The main intention of our interest of LIME to use it for snapshots. I am told that it is a very quick way to make backups. Is that true? Is = there any measuring number for this? =20 >From the recent discussion on snapshots, it seems there are still some = issues, and even a kernel patch. Does RHEL 4 contain such patch? Or is there a downloadable patch if we = buy one? =20 >From what I've read from the Web regarding LIME is that LVM1 is a = read/only while LVM2 is read/write. The read/only mode, if I understand correctly, is that the PE where the = data resides is first copied to an exception table, (is this the COW = table?) before the destination PE is changed. Is this correct? If so, does the = copy involves actual data movement or only a manipulation of of the FAT table? =20 The LVM2's read/write mode seems to simply mark the PE in the snapshot = but the change is not copied from the changed PE to the snapshot, right? =20 In either way, the snapshot seems to be keeping tracks of only the = changes, i.e. delta. Doe we need to first create a full copy of the = file system as the base, or we only need to keep the deltas, if we want = to use snapshot for system backups? =20 Sorry of all the questions, some of them may be pretty basic or = ignorant. If you feel I should get the answers from other sources, I = would really apprecaite it if you can give me the pointer. =20 Alex=20 ________________________________ From: linux-lvm-bounces@redhat.com on behalf of Heinz Mauelshagen Sent: Sat 1/21/2006 09:08 To: LVM general discussion and development Subject: Re: [linux-lvm] Difference in LVM and LVM2 and their = strength/weakness On Fri, Jan 20, 2006 at 05:54:12PM -0800, Alex Chen wrote: > Greetings, Hi. > > I am tasked to investigate the differences between LVM and LVM2. I = am > new to LVM so it would be greatly appreciated if someone can explain = or > point me to the right direction for the following questions: > >=20 > > 1. What does LVM2 have that is not available in LVM? It has command line extensions beyond lvm (eg, vgs, lvs, pvs commands). It's configurable in various regards (eg, device name filters) The limits of 256 grand total logical volumes and ~64k extents per = logical volume are gone. Logical volume snapshots are asynchronous rather than synchronuous and gain better performance. pvmove (online data relocation) is based on temporary, restartable = mirrors which wasn't the case in LVM1. > Or is it a > only better architectured implementation of LVM? I'ld not say 'only', but yes, it is :) > 2. Which version of Red Hat enterprise system uses which LVM? And > does the user need to do any configuration during installation? RHEL3 comes with LVM, RHEL4 with LVM2. > 3. If LVM2 is definitely better than LVM, how stable is it? It is stable with the exception of rare snapshot issues, we're fixing right now. > >=20 > > Thanks. > > Alex > > _______________________________________________ > 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/ -- Regards, Heinz -- The LVM Guy -- *** Software bugs are stupid. Nevertheless it needs not so stupid people to solve them *** =3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D= -=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-= =3D-=3D- Heinz Mauelshagen Red Hat GmbH Consulting Development Engineer Am Sonnenhang 11 Cluster and Storage Development 56242 Marienrachdorf Germany Mauelshagen@RedHat.com +49 2626 141200 FAX 924446 =3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D= -=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-= =3D-=3D- _______________________________________________ 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/ ------_=_NextPart_001_01C61FC3.07ABF28F Content-Type: application/ms-tnef; name="winmail.dat" Content-Transfer-Encoding: base64 eJ8+IiICAQaQCAAEAAAAAAABAAEAAQeQBgAIAAAA5AQAAAAAAADoAAEIgAcAGAAAAElQTS5NaWNy 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SEVJTlosVEhBTktTRk9SVEhFSU5GT1JNQVRJT04vVEhFTUFJTklOVEVOVElPTk9GT1VSSU5URVJF U1RPRkxJTUVUT1VTRUlURk9SU05BUFNIT1RTSUFNVE9MRFRIQVRJVElTQQAAAAACAX8AAQAAAEgA AAA8RThBRkZFRkRCRTk3Qzk0RTkyOTc5NjNGMDUyN0EwN0IwN0FDNzdAcG1pMDBleGYwMC51cy5w YWNrZXRtb3Rpb24uY29tPgDVng== ------_=_NextPart_001_01C61FC3.07ABF28F-- From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 23 Jan 2006 10:40:51 +0100 From: Heinz Mauelshagen Subject: Re: [linux-lvm] Difference in LVM and LVM2 and their strength/weakness Message-ID: <20060123094051.GW2801@redhat.com> References: Mime-Version: 1.0 Content-Disposition: inline In-Reply-To: Reply-To: mauelshagen@redhat.com, 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="us-ascii" Content-Transfer-Encoding: 7bit To: Alex Chen Cc: LVM general discussion and development , mauelshagen@redhat.com On Sun, Jan 22, 2006 at 06:16:33PM -0800, Alex Chen wrote: > Heinz, thanks for the information/ > > The main intention of our interest of LIME to use it for snapshots. > I am told that it is a very quick way to make backups. Is that true? Is there any measuring number for this? Hi Alex, yes, using logical volume snapshots for backups is one of their main purposes. The creation of a snapshot happens instantly (ie. just some allocation for snapshot internal store and some lvm metadata updates which is *fast*). The performance of accessing logical voluems (aka origins) with snapshots largely depends on your io patterns to the origin (ie. heavy writes to the origin slow access to the snapshot down). See remarks below as well. > > >From the recent discussion on snapshots, it seems there are still some issues, and even a kernel patch. > Does RHEL 4 contain such patch? Or is there a downloadable patch if we buy one? We're working on fixes and they'll show up ASAP. > > >From what I've read from the Web regarding LIME is that LVM1 is a read/only while LVM2 is read/write. Correct. > The read/only mode, if I understand correctly, is that the PE where the data resides is first copied to an exception table, (is this the COW table?) > before the destination PE is changed. Is this correct? If so, does the copy involves actual data movement or only a manipulation of > of the FAT table? The exception table holds the information about which chunks (smaller than PEs) have been read off the origin and stored in the exception store before a write to the origin was allowed. That happens at the block devive level and therefore below any filesystem or arbitrary application on top. > The LVM2's read/write mode seems to simply mark the PE in the snapshot but the change is not copied from the changed PE to the snapshot, right? No, any change to the origin leads to a copy *before* the change happens. That's why lots of writes to the origin lead to lots of exceptions and slow down access. If a change to the snapshot is carried out, no copy from the origin is needed, just the expcetion table is updated. > > In either way, the snapshot seems to be keeping tracks of only the changes, i.e. delta. Yes. > Do we need to first create a full copy of the file system as the base, or we only need to keep the deltas, if we want to use snapshot for system backups? The snapshot covers that for you. No user initated copy or anything needed, just create a snapshot, mount (or let your arbitrary application access) it and run your backup on it. > > Sorry of all the questions, some of them may be pretty basic or ignorant. If you feel I should get the answers from other sources, I would really apprecaite it if you can give me the pointer. NP. Heinz > > Alex > > ________________________________ > > From: linux-lvm-bounces@redhat.com on behalf of Heinz Mauelshagen > Sent: Sat 1/21/2006 09:08 > To: LVM general discussion and development > Subject: Re: [linux-lvm] Difference in LVM and LVM2 and their strength/weakness > > > > On Fri, Jan 20, 2006 at 05:54:12PM -0800, Alex Chen wrote: > > Greetings, > > Hi. > > > > > I am tasked to investigate the differences between LVM and LVM2. I am > > new to LVM so it would be greatly appreciated if someone can explain or > > point me to the right direction for the following questions: > > > > > > > > 1. What does LVM2 have that is not available in LVM? > > It has command line extensions beyond lvm (eg, vgs, lvs, pvs commands). > > It's configurable in various regards (eg, device name filters) > > The limits of 256 grand total logical volumes and ~64k extents per logical > volume are gone. > > Logical volume snapshots are asynchronous rather than synchronuous > and gain better performance. > > pvmove (online data relocation) is based on temporary, restartable mirrors > which wasn't the case in LVM1. > > > > Or is it a > > only better architectured implementation of LVM? > > I'ld not say 'only', but yes, it is :) > > > > 2. Which version of Red Hat enterprise system uses which LVM? And > > does the user need to do any configuration during installation? > > RHEL3 comes with LVM, RHEL4 with LVM2. > > > 3. If LVM2 is definitely better than LVM, how stable is it? > > It is stable with the exception of rare snapshot issues, > we're fixing right now. > > > > > > > > > Thanks. > > > > Alex > > > > > _______________________________________________ > > 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/ > > -- > > Regards, > Heinz -- The LVM Guy -- =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Heinz Mauelshagen Red Hat GmbH Consulting Development Engineer Am Sonnenhang 11 Cluster and Storage Development 56242 Marienrachdorf Germany Mauelshagen@RedHat.com +49 2626 141200 FAX 924446 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 23 Jan 2006 13:56:13 +0000 From: "Karl O. Pinc" Subject: Re: [linux-lvm] Difference in LVM and LVM2 and their strength/weakness References: In-Reply-To: (from achen@packetmotion.com on Sun Jan 22 20:16:33 2006) Message-Id: <1138024573l.3950l.2l@mofo> MIME-Version: 1.0 Content-Disposition: inline Content-Transfer-Encoding: 8bit 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="us-ascii"; delsp="Yes"; format="Flowed" To: LVM general discussion and development Cc: mauelshagen@redhat.com On 01/22/2006 08:16:33 PM, Alex Chen wrote: > Heinz, thanks for the information/ > > The main intention of our interest of LIME to use it for snapshots. > I am told that it is a very quick way to make backups. Is that true? (LIME?) To be pedantic, LVM is absolutely not a backup. You can use it to make backups from a known state of the system while the system continues to be updated. Note that unless you've a way to force your appilcations, databases, etc. into a known/internally consistent state at the moment the sanapshot is created this quality is of questionable merit. YMMV. If you trash the filesystem by crashing the disk, etc., your lvm snapshot will be trashed too. Hence, not a backup. See, for example, rsync with --link-dest for a way to make backups from your snapshot that retain snapshot-like disk utilization properties. Karl Free Software: "You don't pay back, you pay forward." -- Robert A. Heinlein From mboxrd@z Thu Jan 1 00:00:00 1970 Content-class: urn:content-classes:message MIME-Version: 1.0 Subject: RE: [linux-lvm] Difference in LVM and LVM2 and their strength/weakness Date: Mon, 23 Jan 2006 11:23:11 -0800 Message-ID: From: "Alex Chen" Content-Transfer-Encoding: 8bit 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="us-ascii" To: mauelshagen@redhat.com Cc: LVM general discussion and development Heinz, Thank you so much for the valuable information. My last questions, I hope, are 1. What commands are need to perform the snapshot and back up? I assume I need to create a snapshot first, (lvmcreate?) Mount that snapshot (mount?) and make back up from it (tar or cpio?) A simple example will be great. 2. Can I do this with Red Hat 9 if I enable LVM1 there? Thanks Alex -----Original Message----- From: Heinz Mauelshagen [mailto:mauelshagen@redhat.com] Sent: Monday, January 23, 2006 1:41 AM To: Alex Chen Cc: mauelshagen@redhat.com; LVM general discussion and development Subject: Re: [linux-lvm] Difference in LVM and LVM2 and their strength/weakness On Sun, Jan 22, 2006 at 06:16:33PM -0800, Alex Chen wrote: > Heinz, thanks for the information/ > > The main intention of our interest of LIME to use it for snapshots. > I am told that it is a very quick way to make backups. Is that true? Is there any measuring number for this? Hi Alex, yes, using logical volume snapshots for backups is one of their main purposes. The creation of a snapshot happens instantly (ie. just some allocation for snapshot internal store and some lvm metadata updates which is *fast*). The performance of accessing logical voluems (aka origins) with snapshots largely depends on your io patterns to the origin (ie. heavy writes to the origin slow access to the snapshot down). See remarks below as well. > > >From the recent discussion on snapshots, it seems there are still some issues, and even a kernel patch. > Does RHEL 4 contain such patch? Or is there a downloadable patch if we buy one? We're working on fixes and they'll show up ASAP. > > >From what I've read from the Web regarding LIME is that LVM1 is a read/only while LVM2 is read/write. Correct. > The read/only mode, if I understand correctly, is that the PE where the data resides is first copied to an exception table, (is this the COW table?) > before the destination PE is changed. Is this correct? If so, does the copy involves actual data movement or only a manipulation of > of the FAT table? The exception table holds the information about which chunks (smaller than PEs) have been read off the origin and stored in the exception store before a write to the origin was allowed. That happens at the block devive level and therefore below any filesystem or arbitrary application on top. > The LVM2's read/write mode seems to simply mark the PE in the snapshot but the change is not copied from the changed PE to the snapshot, right? No, any change to the origin leads to a copy *before* the change happens. That's why lots of writes to the origin lead to lots of exceptions and slow down access. If a change to the snapshot is carried out, no copy from the origin is needed, just the expcetion table is updated. > > In either way, the snapshot seems to be keeping tracks of only the changes, i.e. delta. Yes. > Do we need to first create a full copy of the file system as the base, or we only need to keep the deltas, if we want to use snapshot for system backups? The snapshot covers that for you. No user initated copy or anything needed, just create a snapshot, mount (or let your arbitrary application access) it and run your backup on it. > > Sorry of all the questions, some of them may be pretty basic or ignorant. If you feel I should get the answers from other sources, I would really apprecaite it if you can give me the pointer. NP. Heinz > > Alex > > ________________________________ > > From: linux-lvm-bounces@redhat.com on behalf of Heinz Mauelshagen > Sent: Sat 1/21/2006 09:08 > To: LVM general discussion and development > Subject: Re: [linux-lvm] Difference in LVM and LVM2 and their strength/weakness > > > > On Fri, Jan 20, 2006 at 05:54:12PM -0800, Alex Chen wrote: > > Greetings, > > Hi. > > > > > I am tasked to investigate the differences between LVM and LVM2. I am > > new to LVM so it would be greatly appreciated if someone can explain or > > point me to the right direction for the following questions: > > > > > > > > 1. What does LVM2 have that is not available in LVM? > > It has command line extensions beyond lvm (eg, vgs, lvs, pvs commands). > > It's configurable in various regards (eg, device name filters) > > The limits of 256 grand total logical volumes and ~64k extents per logical > volume are gone. > > Logical volume snapshots are asynchronous rather than synchronuous > and gain better performance. > > pvmove (online data relocation) is based on temporary, restartable mirrors > which wasn't the case in LVM1. > > > > Or is it a > > only better architectured implementation of LVM? > > I'ld not say 'only', but yes, it is :) > > > > 2. Which version of Red Hat enterprise system uses which LVM? And > > does the user need to do any configuration during installation? > > RHEL3 comes with LVM, RHEL4 with LVM2. > > > 3. If LVM2 is definitely better than LVM, how stable is it? > > It is stable with the exception of rare snapshot issues, > we're fixing right now. > > > > > > > > > Thanks. > > > > Alex > > > > > _______________________________________________ > > 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/ > > -- > > Regards, > Heinz -- The LVM Guy -- =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- =-=-=- Heinz Mauelshagen Red Hat GmbH Consulting Development Engineer Am Sonnenhang 11 Cluster and Storage Development 56242 Marienrachdorf Germany Mauelshagen@RedHat.com +49 2626 141200 FAX 924446 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- =-=-=- From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 23 Jan 2006 22:23:39 +0100 From: Heinz Mauelshagen Subject: Re: [linux-lvm] Difference in LVM and LVM2 and their strength/weakness Message-ID: <20060123212339.GC2801@redhat.com> References: Mime-Version: 1.0 Content-Disposition: inline In-Reply-To: Reply-To: mauelshagen@redhat.com, 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="us-ascii" Content-Transfer-Encoding: 7bit To: Alex Chen Cc: LVM general discussion and development , mauelshagen@redhat.com On Mon, Jan 23, 2006 at 11:23:11AM -0800, Alex Chen wrote: > Heinz, > Thank you so much for the valuable information. > > My last questions, I hope, are > > 1. What commands are need to perform the snapshot and back up? > I assume I need to create a snapshot first, (lvmcreate?) > Mount that snapshot (mount?) and make back up from it (tar or cpio?) > A simple example will be great. See lvcreate manual (-s option), mount and use whatever backup program of your choice. Say your existing logical volume is called /dev/VG/LV and is 100GB large, make a snapshot with a 6GB exception store (5-10% is ususally a good size): # lvcreate -s -L6G -n SNAP /dev/VG/LV # mkdir /mnt/SNAP # mount -r /dev/VG/SNAP /mnt/SNAP # cd /mnt/SNAP # find .|cpio -o ... # cd # umount /mnt/SNAP # lvremove /dev/VG/SNAP > > 2. Can I do this with Red Hat 9 if I enable LVM1 there? Yes. Regards, Heinz > > Thanks > > Alex > > -----Original Message----- > From: Heinz Mauelshagen [mailto:mauelshagen@redhat.com] > Sent: Monday, January 23, 2006 1:41 AM > To: Alex Chen > Cc: mauelshagen@redhat.com; LVM general discussion and development > Subject: Re: [linux-lvm] Difference in LVM and LVM2 and their > strength/weakness > > On Sun, Jan 22, 2006 at 06:16:33PM -0800, Alex Chen wrote: > > Heinz, thanks for the information/ > > > > The main intention of our interest of LIME to use it for snapshots. > > I am told that it is a very quick way to make backups. Is that true? > Is there any measuring number for this? > > Hi Alex, > > yes, using logical volume snapshots for backups is one of their main > purposes. > > The creation of a snapshot happens instantly (ie. just some allocation > for > snapshot internal store and some lvm metadata updates which is *fast*). > > The performance of accessing logical voluems (aka origins) with > snapshots > largely depends on your io patterns to the origin (ie. heavy writes to > the > origin slow access to the snapshot down). See remarks below as well. > > > > > > >From the recent discussion on snapshots, it seems there are still > some issues, and even a kernel patch. > > Does RHEL 4 contain such patch? Or is there a downloadable patch if > we buy one? > > We're working on fixes and they'll show up ASAP. > > > > > >From what I've read from the Web regarding LIME is that LVM1 is a > read/only while LVM2 is read/write. > > Correct. > > > The read/only mode, if I understand correctly, is that the PE where > the data resides is first copied to an exception table, (is this the COW > table?) > > before the destination PE is changed. Is this correct? If so, does > the copy involves actual data movement or only a manipulation of > > of the FAT table? > > The exception table holds the information about which chunks (smaller > than PEs) > have been read off the origin and stored in the exception store before a > write > to the origin was allowed. > > That happens at the block devive level and therefore below any > filesystem > or arbitrary application on top. > > > The LVM2's read/write mode seems to simply mark the PE in the snapshot > but the change is not copied from the changed PE to the snapshot, right? > > No, any change to the origin leads to a copy *before* the change > happens. > That's why lots of writes to the origin lead to lots of exceptions and > slow > down access. > If a change to the snapshot is carried out, no copy from the origin is > needed, > just the expcetion table is updated. > > > > > In either way, the snapshot seems to be keeping tracks of only the > changes, i.e. delta. > > Yes. > > > Do we need to first create a full copy of the file system as the base, > or we only need to keep the deltas, if we want to use snapshot for > system backups? > > The snapshot covers that for you. No user initated copy or anything > needed, > just create a snapshot, mount (or let your arbitrary application access) > it and run your backup on it. > > > > > Sorry of all the questions, some of them may be pretty basic or > ignorant. If you feel I should get the answers from other sources, I > would really apprecaite it if you can give me the pointer. > > NP. > > Heinz > > > > > Alex > > > > ________________________________ > > > > From: linux-lvm-bounces@redhat.com on behalf of Heinz Mauelshagen > > Sent: Sat 1/21/2006 09:08 > > To: LVM general discussion and development > > Subject: Re: [linux-lvm] Difference in LVM and LVM2 and their > strength/weakness > > > > > > > > On Fri, Jan 20, 2006 at 05:54:12PM -0800, Alex Chen wrote: > > > Greetings, > > > > Hi. > > > > > > > > I am tasked to investigate the differences between LVM and LVM2. > I am > > > new to LVM so it would be greatly appreciated if someone can explain > or > > > point me to the right direction for the following questions: > > > > > > > > > > > > 1. What does LVM2 have that is not available in LVM? > > > > It has command line extensions beyond lvm (eg, vgs, lvs, pvs > commands). > > > > It's configurable in various regards (eg, device name filters) > > > > The limits of 256 grand total logical volumes and ~64k extents per > logical > > volume are gone. > > > > Logical volume snapshots are asynchronous rather than synchronuous > > and gain better performance. > > > > pvmove (online data relocation) is based on temporary, restartable > mirrors > > which wasn't the case in LVM1. > > > > > > > Or is it a > > > only better architectured implementation of LVM? > > > > I'ld not say 'only', but yes, it is :) > > > > > > > 2. Which version of Red Hat enterprise system uses which LVM? > And > > > does the user need to do any configuration during installation? > > > > RHEL3 comes with LVM, RHEL4 with LVM2. > > > > > 3. If LVM2 is definitely better than LVM, how stable is it? > > > > It is stable with the exception of rare snapshot issues, > > we're fixing right now. > > > > > > > > > > > > > > Thanks. > > > > > > Alex > > > > > > > > _______________________________________________ > > > 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/ > > > > -- > > > > Regards, > > Heinz -- The LVM Guy -- =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Heinz Mauelshagen Red Hat GmbH Consulting Development Engineer Am Sonnenhang 11 Cluster and Storage Development 56242 Marienrachdorf Germany Mauelshagen@RedHat.com +49 2626 141200 FAX 924446 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-