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 412A9EE38A for ; Sat, 5 Sep 2020 11:47:26 +0000 (UTC) Received: from us-smtp-1.mimecast.com (us-smtp-1.mimecast.com [205.139.110.61]) (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 C5AD8811E76 for ; Sat, 5 Sep 2020 11:47:26 +0000 (UTC) MIME-Version: 1.0 Date: Sat, 05 Sep 2020 13:47:15 +0200 From: Gionatan Danti In-Reply-To: <79061390.1069833.1599071934227.JavaMail.zimbra@karlsbakk.net> References: <79061390.1069833.1599071934227.JavaMail.zimbra@karlsbakk.net> Message-ID: <53661d4eefb635710b51cf9bfee894ef@assyoma.it> Content-Transfer-Encoding: 7bit Subject: Re: [linux-lvm] Looking ahead - tiering with LVM? 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: Roy Sigurd Karlsbakk , =?UTF-8?Q?H=C3=A5kon?= Il 2020-09-02 20:38 Roy Sigurd Karlsbakk ha scritto: > Hi all > > I just wonder how it could be possible some day, some year, to make > lvm use tiering. I guess this has been debated numerous times before > and I found this lvmts project, but it hasn't been updated for eight > years or so. Hi, having developed and supported file-level form of tiered storage in response to a specific customer request, I have the feeling that tiered storage (both file and block based) is not so useful as it seems. Let me explain why I feel so... The key difference between caching and tiering is that the former does not increase total available space, while the latter provides as much space as available in each storage tier. For example, 1 TB SSD + 10 TB HDD can be combined for a 11 TB tiered volume. Tiering is useful when the faster volume provides a significant portion of the total aggregated sum - which is often not the case. In the example above, the SSD only provides a 10% space increase over plain caching. You can argue that one can simple enlarge the performane tier, for example using a 4 TB SSD + 10 TB HDD, but you are now in the ballpark of affording a full-SSD volume - ditching *both* tiering and caching. That said, LVM already provides the basic building block to provide tiering as you can pvmove between block devices. The difficult thing is how to determine which block to move, and managing them in an automated way. 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