From mboxrd@z Thu Jan 1 00:00:00 1970 References: <2d496550-4609-0a26-489b-8721737c783b@redhat.com> <257A9B1C-04AC-4EDE-9671-9E7A60104F9F@gmail.com> From: Zdenek Kabelac Message-ID: Date: Tue, 15 Sep 2020 23:47:53 +0200 MIME-Version: 1.0 In-Reply-To: <257A9B1C-04AC-4EDE-9671-9E7A60104F9F@gmail.com> Content-Language: en-US Content-Transfer-Encoding: quoted-printable Subject: Re: [linux-lvm] lvm limitations 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="iso-8859-1"; format="flowed" To: =?UTF-8?Q?Tomas_Dalebj=c3=b6rk?= Cc: LVM general discussion and development , Gionatan Danti Dne 15. 09. 20 v 23:24 Tomas Dalebj=C3=B6rk napsal(a): > thanks >=20 > ok, lets say that I have 10 LV on a server, and want create a thin lv sna= pshot every hour and keep that for 30 days > that would be 24h * 30days * 10lv =3D 720 lv >=20 > if I want to keep snapshot copies from more nodes, to serve a single repo= sitory of snapshot copies, than these would easily become several hundred t= housands of lv >=20 > not sure if this is a good idea, but I guess it can be very useful in som= e sense as block level incremental forever and instant recovery can be impl= emented for open sourced based applications >=20 > what reflections do you have on this idea? Hi You likely don't need such amount of 'snapshots' and you will need to=20 implement something to remove snapshot without need, so i.e. after a day yo= u=20 will keep maybe 'every-4-hour' and after couple days maybe only a day-level= =20 snapshot. After a month per-week and so one. You need to be aware that as soon as your volumes have some 'real-live' you will soon need to keep many blocks in many 'different' copies which will surely be reflected by the usage of the pool device itself - aka you will most likely hit out-of-space sooner then you'll run out of devices. Speaking of thin volumes - there can be at most 2^24 thin devices (this is hard limit you've ask for ;)) - but you have only ~16GiB of metad= ata=20 to store all of them - which gives you ~1KiB of data per such volume - quite frankly this is not too much - unless as said - your volumes are not changed at all - but then why you would be building all this... That all said - if you really need that intensive amount of snapshoting, lvm2 is likely not for you - and you will need to build something on your o= wn, as you will need way more efficient and 'targeted' solution for your purpos= e. There is no practical way to change current LVM2 into a tool handling i.e. = 100.000 LV at decent speed - it's never been a target of this tool.... Regards Zdenek