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 3E48A2166BA0 for ; Wed, 9 Sep 2020 20:20:55 +0000 (UTC) Received: from us-smtp-1.mimecast.com (us-smtp-2.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 EB78D101A53F for ; Wed, 9 Sep 2020 20:20:54 +0000 (UTC) MIME-Version: 1.0 Date: Wed, 09 Sep 2020 22:20:48 +0200 From: Gionatan Danti In-Reply-To: <24409.12987.382863.95686@quad.stoffel.home> References: <79061390.1069833.1599071934227.JavaMail.zimbra@karlsbakk.net> <53661d4eefb635710b51cf9bfee894ef@assyoma.it> <83152674.4938205.1599663690759.JavaMail.zimbra@karlsbakk.net> <3503b4f5b55345beb24de4b156ee75c7@assyoma.it> <24409.9033.527504.36789@quad.stoffel.home> <7d62cb86425416d5a3db115afdbd996c@assyoma.it> <24409.12987.382863.95686@quad.stoffel.home> 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: John Stoffel Cc: Sigurd Karlsbakk , Roy, =?UTF-8?Q?H=C3=A5kon?= , LVM general discussion and development Il 2020-09-09 21:53 John Stoffel ha scritto: > Very true, numbers talk, annecdotes walk... Sure - lets try to gather some numbers from the data you posted before... > sudo lvcache status data/home > +-----------------------+------------------+ > | Field | Value | > +-----------------------+------------------+ > | cached | True | > | size | 806380109824 | > | cache_lv | home_cache | > | cache_lv_size | 85899345920 | You cache device is squarely in the 10x ballpark (ie: it is ~9.39x smaller than your SSD). Having ~10.64% more space would be nice, but hardly game-changer. > | read_hits | 138697828 | > | read_misses | 7874434 | You have 94.6% hit rate from your hotspot cache - compare this to an ideally managed tiered storage, with its 100% (ideal, not reasonable in real world) hit rate. Does it really change anything? > | write_hits | 777455171 | > | write_misses | 9841866 | And you have an even better ~98.7% write hit ratio. As you have a mirrored cache device, you should be able to set LVM for using a writeback cache without risking your data in case of a single cache drive failure. I suspect this would do wonder with your hit ratio - but again, testing is the only method to be sure. Thanks for sharing your data! 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