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 4CCC42166BA0 for ; Wed, 9 Sep 2020 18:54:08 +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 DD4BE18AE949 for ; Wed, 9 Sep 2020 18:54:08 +0000 (UTC) MIME-Version: 1.0 Message-ID: <24409.9033.527504.36789@quad.stoffel.home> Date: Wed, 9 Sep 2020 14:47:37 -0400 From: "John Stoffel" In-Reply-To: <3503b4f5b55345beb24de4b156ee75c7@assyoma.it> References: <79061390.1069833.1599071934227.JavaMail.zimbra@karlsbakk.net> <53661d4eefb635710b51cf9bfee894ef@assyoma.it> <83152674.4938205.1599663690759.JavaMail.zimbra@karlsbakk.net> <3503b4f5b55345beb24de4b156ee75c7@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" To: LVM general discussion and development Cc: Roy Sigurd Karlsbakk , =?iso-8859-1?Q?H=E5kon?= >>>>> "Gionatan" == Gionatan Danti writes: Gionatan> Il 2020-09-09 17:01 Roy Sigurd Karlsbakk ha scritto: >> 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. Gionatan> It really depends on the use case. I applied it to a Gionatan> fileserver, so working at file level was the right Gionatan> choice. For VMs (or big files) it is useless, I agree. This assumes you're tiering whole files, not at the per-block level though, right? >> This is all known. Gionatan> But the only reason to want tiering vs cache is the Gionatan> additional space the former provides. If this additional Gionatan> space is so small (compared to the combined, total volume Gionatan> space), tiering's advantage shrinks to (almost) nothing. Do you have numbers? I'm using DM_CACHE on my home NAS server box, and it *does* seem to help, but only in certain cases. I've got a 750gb home directory LV with an 80gb lv_cache writethrough cache setup. So it's not great on write heavy loads, but it's good in read heavy ones, such as kernel compiles where it does make a difference. So it's not only the caching being per-file or per-block, but how the actual cache is done? writeback is faster, but less reliable if you crash. Writethrough is slower, but much more reliable.