From: Zdenek Kabelac <firstname.lastname@example.org> To: LVM general discussion and development <email@example.com>, John Stoffel <firstname.lastname@example.org> Cc: "Roy Sigurd Karlsbakk" <email@example.com>, Håkon <firstname.lastname@example.org> Subject: Re: [linux-lvm] Looking ahead - tiering with LVM? Date: Wed, 9 Sep 2020 21:10:13 +0200 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <firstname.lastname@example.org> Dne 09. 09. 20 v 20:47 John Stoffel napsal(a): >>>>>> "Gionatan" == Gionatan Danti <email@example.com> writes: > > Gionatan> Il 2020-09-09 17:01 Roy Sigurd Karlsbakk ha scritto: >>> First, filelevel is usually useless. Say you have 50 VMs with Windows >>> server something. A lot of them are bound to have a ton of equal >>> storage in the same areas, but the file size and content will vary >>> over time. With blocklevel tiering, that could work better. > > Gionatan> It really depends on the use case. I applied it to a > Gionatan> fileserver, so working at file level was the right > Gionatan> choice. For VMs (or big files) it is useless, I agree. > > This assumes you're tiering whole files, not at the per-block level > though, right? > >>> This is all known. > > Gionatan> But the only reason to want tiering vs cache is the > Gionatan> additional space the former provides. If this additional > Gionatan> space is so small (compared to the combined, total volume > Gionatan> space), tiering's advantage shrinks to (almost) nothing. > > Do you have numbers? I'm using DM_CACHE on my home NAS server box, > and it *does* seem to help, but only in certain cases. I've got a > 750gb home directory LV with an 80gb lv_cache writethrough cache > setup. So it's not great on write heavy loads, but it's good in read > heavy ones, such as kernel compiles where it does make a difference. > > So it's not only the caching being per-file or per-block, but how the > actual cache is done? writeback is faster, but less reliable if you > crash. Writethrough is slower, but much more reliable. Hi dm-cache (--type cache) is hotspot cache (most used areas of device) dm-writecache (--type writecache) is great with write-extensive load (somewhat extends your page cache on your NMVe/SSD/persistent-memory) We were thinking about layering cached above each other - but so far there was no big demand and also the complexity of solving problem is rising greatly - aka there is no problem to let users to stack cache on top of another cache on top of 3rd. cache - but what should have when it starts failing... AFAIK there is no one yet writing driver for combining i.e. SSD + HDD into a single drive which would be relocating blocks (so you get total size as aproximate sum of both devices) - but there is dm-zoned which solves somewhat similar problem - but I've no experience with that... Zdenek
next prev parent reply other threads:[~2020-09-09 19:10 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-09-02 18:38 Roy Sigurd Karlsbakk 2020-09-05 11:47 ` Gionatan Danti 2020-09-09 15:01 ` Roy Sigurd Karlsbakk 2020-09-09 18:16 ` Gionatan Danti 2020-09-09 18:47 ` John Stoffel 2020-09-09 19:10 ` Zdenek Kabelac [this message] 2020-09-09 19:21 ` John Stoffel 2020-09-09 19:44 ` Gionatan Danti 2020-09-09 19:53 ` John Stoffel 2020-09-09 20:20 ` Gionatan Danti 2020-09-09 19:41 ` Roy Sigurd Karlsbakk 2020-09-09 19:49 ` Gionatan Danti
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --subject='Re: [linux-lvm] Looking ahead - tiering with LVM?' \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).