From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christopher James Halse Rogers Subject: Re: How to create bcachefs? Date: Thu, 25 Aug 2016 21:09:54 +1000 Message-ID: <1472123394.15072.7@mail.cooperteam.net> References: <20160824065212.fzs2nk3rg7z7iudb@kmo-pixel> <1472083387.31787.0@mail.cooperteam.net> <2f1e41df-3f3e-0115-e21b-2f1fb2148934@mejor.pl> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-13; format=flowed Content-Transfer-Encoding: quoted-printable Return-path: Received: from mail.cooperteam.net ([150.101.105.211]:34974 "EHLO mail.cooperteam.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752567AbcHYLS2 (ORCPT ); Thu, 25 Aug 2016 07:18:28 -0400 In-Reply-To: <2f1e41df-3f3e-0115-e21b-2f1fb2148934@mejor.pl> Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: Marcin =?UTF-8?b?TWlyb3PFgmF3?= Cc: linux-bcache@vger.kernel.org On Thu, Aug 25, 2016 at 7:21 PM, Marcin Miros=C5=82aw =20 wrote: > W dniu 25.08.2016 o 02:03, Christopher James Halse Rogers pisze: >=20 > Hi! >=20 >> On Thu, Aug 25, 2016 at 7:21 AM, marcin@mejor.pl wrote: > [...] >>> Does it means that cache is unavailable and only tiering will be in >>> bcachefs? >>> And... How to mount tiered FS? When I pass one device in mount I'm >>> getting: >>> bcache: bch_open_as_blockdevs() register_cache_set err=20 >>> insufficient >>> devices >>=20 >> Tiering gets you all the advantages of caching, plus you can (with=20 >> some >> effort) have the combined filesystem size be the sum of the SSD +=20 >> HDD >> capacities, rather than the capacity be determined solely by the >> capacity of the slow tier (this is not currently the case for=20 >> bcachefs). >=20 > I think that cacheing has at least such advantages over tiering: > - allow fast read and write to files compressed with slow alghoritm=20 > (gzip) I think this is getting into =E2=80=9Cwhat should we call this thing=E2=80= =9D=20 arguments. A naive cache is just going to promote the gzipped data to=20 the fast storage. On the other end, there's nothing much preventing a=20 sophisticated tiering system from compressing/decompressing as a part=20 of tier demotion/promotion. > - can be optimized for using SSD drives It's not clear to me how? Tiering and caching are doing the same sort=20 of things. =