From owner-freebsd-questions@freebsd.org Tue Dec 19 14:46:11 2017 Return-Path: Delivered-To: freebsd-questions@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id BE9D1E87ADA for ; Tue, 19 Dec 2017 14:46:11 +0000 (UTC) (envelope-from rwmaillists@googlemail.com) Received: from mail-wm0-x22b.google.com (mail-wm0-x22b.google.com [IPv6:2a00:1450:400c:c09::22b]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 584627B8B5 for ; Tue, 19 Dec 2017 14:46:11 +0000 (UTC) (envelope-from rwmaillists@googlemail.com) Received: by mail-wm0-x22b.google.com with SMTP id t8so4147571wmc.3 for ; Tue, 19 Dec 2017 06:46:11 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:subject:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=UTyJNxjYuaO+8gRZjHBVOowXELdtl/htiv3Kw0rH77s=; b=uT8Vyt/wxbtMEM+CvA7b70xLdN9ydgQVZul8uE90/rZdjjJrk2NjpbNcUraSwXXner wchnokeYmQ2j56fjI3afKrPxTiWMwn1Ja9I9IxcmOHxtHl8LbqrkfZP4J3/MhHt0UHQg bAV9422F8sfzHnks++QlS9iwNleP37oqz4zVyqHL8UBR+Zgz0UP8zNUJ47cJKVHFGm6f 7Oz8aAQP4FbEU1M4MUNemIxWN+3mjqULh3/lgEn33amdbGIfdxJLnczvfn4qR0WMDIVI sLpO6CKjvb3wjQafQ633s6z8XDrFyydzwjqcf7uiFBC1NLIaFp8RRc5s5lUzrmkH3xuu 0ebA== X-Gm-Message-State: AKGB3mIVAHLPsNeMGY5kW4ndsloljvVX6Jtgc0HPR2s+NP4u4m9QTsbR mI4HCCTgCWwHGsDS8pGNVfx7IQ== X-Google-Smtp-Source: ACJfBosV8RhzjvFM+G2Z+bc+Lk+HkK0/ois0kj7Mp1lUjcx+j1tK/D8eXeg9huN5w1hls93p9MPzCw== X-Received: by 10.80.222.73 with SMTP id a9mr921573edl.214.1513694769454; Tue, 19 Dec 2017 06:46:09 -0800 (PST) Received: from gumby.homeunix.com ([81.17.24.158]) by smtp.gmail.com with ESMTPSA id h56sm12770184eda.97.2017.12.19.06.46.08 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 19 Dec 2017 06:46:08 -0800 (PST) Date: Tue, 19 Dec 2017 14:46:06 +0000 From: RW To: freebsd-questions@freebsd.org Subject: Re: hd firecuda Message-ID: <20171219144606.0217ee55@gumby.homeunix.com> In-Reply-To: <20171219081418.5672730b.freebsd.ed.lists@sumeritec.com> References: <1513447749.62024.1.camel@yandex.com> <20171217112428.150d8041.freebsd.ed.lists@sumeritec.com> <20171217111319.6a1af590@gumby.homeunix.com> <20171217194753.3ab59e6d.freebsd.ed.lists@sumeritec.com> <20171217150007.642efc20@gumby.homeunix.com> <20171218085219.2fec7c3b.freebsd.ed.lists@sumeritec.com> <20171218162625.5bcc543e@gumby.homeunix.com> <20171219081418.5672730b.freebsd.ed.lists@sumeritec.com> X-Mailer: Claws Mail 3.15.1 (GTK+ 2.24.31; amd64-portbld-freebsd11.1) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 19 Dec 2017 14:46:11 -0000 On Tue, 19 Dec 2017 08:14:18 +0800 Erich Dollansky wrote: On Tue, 19 Dec 2017 08:14:18 +0800 Erich Dollansky wrote: > Hi, > > On Mon, 18 Dec 2017 16:26:25 +0000 > RW via freebsd-questions wrote: > > The details of precisely which sectors are cached is not important > > (although it is important to recognise that Seagate doesn't care > > about how these devices perform under FreeBSD). > > > > What I'm getting at is that previous version of these devices did > > selective read caching - not write caching. I don't see any reason > > to think that this has changed - especially when their marketing > > isn't mentioning it. > > > > Even if they are now doing write caching, it's very unlikely that > > anything like the full 8GB of flash would available for it because > > you wouldn't want saving a 10GB video file to blow-away the > > cache. > Seagate is very silent about how the FireCuda actually stores data on > the disk. It uses a technology called SMR. ... > The drives can now use a reserved space of the disk to store the data. > On long writes, this space will also be filled. It's unlikely that it would fall back to discarding useful cache in the SSD *after* filling the larger non-shingled area of the drive. If that bit of extra buffering made a useful difference they'd just increase the size of the non-shingled area. > It could be also that > the disk fills first SSD and then the reserved space. If that happened I'd expect the speed to first drop to an intermediate speed of 50-100 MB/s, where the the non-shingled area is being written to, and then drop again when the non-shingled area fills. IMO what you are seeing is consistent with selective read caching plus write caching into the non-shingled area.