From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mimecast-mx02.redhat.com (mimecast06.extmail.prod.ext.rdu2.redhat.com [10.11.55.22]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 06FD1E77BC for ; Wed, 9 Sep 2020 15:01:42 +0000 (UTC) Received: from us-smtp-1.mimecast.com (us-smtp-delivery-1.mimecast.com [207.211.31.120]) (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 A02F118AE956 for ; Wed, 9 Sep 2020 15:01:42 +0000 (UTC) Date: Wed, 9 Sep 2020 17:01:30 +0200 (CEST) From: Roy Sigurd Karlsbakk Message-ID: <83152674.4938205.1599663690759.JavaMail.zimbra@karlsbakk.net> In-Reply-To: <53661d4eefb635710b51cf9bfee894ef@assyoma.it> References: <79061390.1069833.1599071934227.JavaMail.zimbra@karlsbakk.net> <53661d4eefb635710b51cf9bfee894ef@assyoma.it> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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="utf-8" To: linux-lvm Cc: =?utf-8?Q?H=C3=A5kon?= >> 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... First, filelevel is usually useless. Say you have 50 VMs with Windows server something. A lot of them are bound to have a ton of equal storage in the same areas, but the file size and content will vary over time. With blocklevel tiering, that could work better. > 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. This is all known. > 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. If you look at IOPS instead of just sequencial speed, you'll see the difference. A set of 10 drives in a RAID-6 will perhaps, maybe, give you 1kIOPS, while a single SSD might give you 50kIOPS or even more. This makes a huge impact. > 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. …which was the reason I asked this question, and which should be quite clear in the original post. Vennlig hilsen roy -- Roy Sigurd Karlsbakk (+47) 98013356 http://blogg.karlsbakk.net/ GPG Public key: http://karlsbakk.net/roysigurdkarlsbakk.pubkey.txt -- Hið góða skaltu í stein höggva, hið illa í snjó rita.