From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mimecast-mx02.redhat.com (mimecast03.extmail.prod.ext.rdu2.redhat.com [10.11.55.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C2C152166B2C for ; Mon, 23 Nov 2020 12:47:10 +0000 (UTC) Received: from us-smtp-1.mimecast.com (us-smtp-delivery-1.mimecast.com [205.139.110.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7369E811E76 for ; Mon, 23 Nov 2020 12:47:10 +0000 (UTC) MIME-Version: 1.0 Date: Mon, 23 Nov 2020 13:44:03 +0100 From: Gionatan Danti In-Reply-To: References: Message-ID: <6ea77fe7d910218bb46367f35d1a19a6@assyoma.it> Content-Transfer-Encoding: 7bit Subject: Re: [linux-lvm] What is the use of thin snapshots if the external origin cannot be set to writable ? 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"; format="flowed" To: LVM general discussion and development Cc: Sreyan Chakravarty Il 2020-11-21 04:10 Sreyan Chakravarty ha scritto: > I mean what is the point of creating a snapshot if I can't change my > original volume ? > > Is there some sort of resolution ? External thin snapshot are useful to share a common, read-only base (ie: a "gold-master" image) with different writable thin lvm overlay volumes. They can not be merged into external origin; otherwise, a single merge operation would invalidate *all* other thin snapshot relying on the same origin. Classical LVM snapshots are good for temporary, short-lived snapshots - basically taken for backup purpose only (and immediately removed after the backup completed). You should not use them for long-lived snapshots (otherwise you can see much lower performance and delayed boot). If you want to have long-lived snapshot you should use LVM thin snapshots. For root volumes, you have two choices: - use a thin lvm volume for root, which is a supported use case (but it will probably require a system reinstallation); - continue using your classical LVM as a immutable base and use a thin lvm with external snapshot to store all new writes. Regards. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8