From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mimecast-mx02.redhat.com (mimecast04.extmail.prod.ext.rdu2.redhat.com [10.11.55.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 27BF92157F25 for ; Wed, 9 Sep 2020 19:49:52 +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 3D26F101A569 for ; Wed, 9 Sep 2020 19:49:52 +0000 (UTC) MIME-Version: 1.0 Date: Wed, 09 Sep 2020 21:49:31 +0200 From: Gionatan Danti In-Reply-To: <695805084.5038574.1599680480630.JavaMail.zimbra@karlsbakk.net> References: <79061390.1069833.1599071934227.JavaMail.zimbra@karlsbakk.net> <53661d4eefb635710b51cf9bfee894ef@assyoma.it> <83152674.4938205.1599663690759.JavaMail.zimbra@karlsbakk.net> <3503b4f5b55345beb24de4b156ee75c7@assyoma.it> <695805084.5038574.1599680480630.JavaMail.zimbra@karlsbakk.net> Message-ID: 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 2020-09-09 21:41 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 >>> 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. >> >> IOPs are already well server by LVM cache. So, I genuinely ask: what >> would be tiering advantage here? I'll love to ear a reasonable use >> case. > > LVMcache only helps if the cache is there in the first place and IIRC > it's cleared after a reboot. I seem to remember that cache is persistent, but a writeback cache must be flushed to the underlying disk in case of unclean shutdown. This, however, should not empty the cache itself. > It help won't that much over time with large storage. It also wastes > space. I tend to disagree: with large storage, you really want an hotspot cache vs a tiered approach unless: a) the storage tiers are comparable in size, which is quite rare; b) the slow storage does some sort of offline compression/deduplication, with the faster layer being a landing zone for newly ingested data. Can you describe a reasonable real-world setup where plain LVM tiering would be useful? Again, this is a genuine question: I am interested in different storage setup than mine. Thanks. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8