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From: Gionatan Danti <g.danti@assyoma.it>
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, 09 Sep 2020 21:49:31 +0200	[thread overview]
Message-ID: <daf74778e6b44904e6a07a4e38c8c03a@assyoma.it> (raw)
In-Reply-To: <695805084.5038574.1599680480630.JavaMail.zimbra@karlsbakk.net>

Il 2020-09-09 21:41 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
>>> If you look at IOPS instead of just sequencial speed, you'll see the
>>> difference. A set of 10 drives in a RAID-6 will perhaps, maybe, give
>>> you 1kIOPS, while a single SSD might give you 50kIOPS or even more.
>>> This makes a huge impact.
>> 
>> IOPs are already well server by LVM cache. So, I genuinely ask: what
>> would be tiering advantage here? I'll love to ear a reasonable use 
>> case.
> 
> LVMcache only helps if the cache is there in the first place and IIRC
> it's cleared after a reboot.

I seem to remember that cache is persistent, but a writeback cache must 
be flushed to the underlying disk in case of unclean shutdown. This, 
however, should not empty the cache itself.

> It help won't that much over time with large storage. It also wastes 
> space.

I tend to disagree: with large storage, you really want an hotspot cache 
vs a tiered approach unless:
a) the storage tiers are comparable in size, which is quite rare;
b) the slow storage does some sort of offline compression/deduplication, 
with the faster layer being a landing zone for newly ingested data.

Can you describe a reasonable real-world setup where plain LVM tiering 
would be useful? Again, this is a genuine question: I am interested in 
different storage setup than mine.

Thanks.

-- 
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8

      reply	other threads:[~2020-09-09 19:49 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
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 [this message]

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