From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Casier AEVOO Subject: Re: [Documentation] Hardware recommandation : RAM and PGLog Date: Tue, 21 Jul 2015 17:00:14 +0200 Message-ID: <55AE5E7E.9050806@aevoo.fr> References: <55ABC8E5.1030304@aevoo.fr> <55ABCB49.1080304@aevoo.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from 62-210-192-203.rev.poneytelecom.eu ([62.210.192.203]:41938 "EHLO aevoo.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752861AbbGUPBM (ORCPT ); Tue, 21 Jul 2015 11:01:12 -0400 In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: ceph-devel@vger.kernel.org Cc: Sage Weil OK, I just understand the need of transactions for the trim takes place after changing settings. What is the risk to have too low a value for the parameter osd_min_pg_log_entries (not osd_max_pg_log_entries in degraded environment) ? David. On 07/20/2015 03:13 PM, Sage Weil wrote: > On Sun, 19 Jul 2015, David Casier AEVOO wrote: >> Hi, >> I have a question about PGLog and RAM consumption. >> >> In the documentation, we read "OSDs do not require as much RAM for regular >> operations (e.g., 500MB of RAM per daemon instance); however, during recovery >> they need significantly more RAM (e.g., ~1GB per 1TB of storage per daemon)" >> >> But in fact, all pg log are read in the start of ceph-osd daemon and put in >> RAM ( pg->read_state(store, bl); ) >> >> Is this normal behavior or I have a defect in my environment? > There are two tunables that control how many pg log entries we keep > around. When teh PG is healthy, we keep ~1000, and when the PG is > degraded, we keep more, to expand the time window over which a recovering > OSD will be able to do regular log-based recovery instead of a more > expensive backfill. This is one source of additional memory. > > Others are the missing sets (lists of missing/degraded objects) and > messages/data/state associated with objcts that are being > recovered/copied. > > Note that the numbers in teh documentation are pretty rough rules of > thumb. At some point it would be great to build a model for how much RAM > the osd consumes as a function of the various configurables (pg log size, > pg count, avg object size, etc.). > > sage > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html