From: "John Stoffel" <john@stoffel.org>
To: LVM general discussion and development <linux-lvm@redhat.com>
Cc: "Roy Sigurd Karlsbakk" <roy@karlsbakk.net>, Håkon <hawken@thehawken.org>
Subject: Re: [linux-lvm] Looking ahead - tiering with LVM?
Date: Wed, 9 Sep 2020 14:47:37 -0400 [thread overview]
Message-ID: <24409.9033.527504.36789@quad.stoffel.home> (raw)
In-Reply-To: <3503b4f5b55345beb24de4b156ee75c7@assyoma.it>
>>>>> "Gionatan" == Gionatan Danti <g.danti@assyoma.it> 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.
next prev parent reply other threads:[~2020-09-09 18:54 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 [this message]
2020-09-09 19:10 ` Zdenek Kabelac
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
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