From: Gionatan Danti <g.danti@assyoma.it>
To: John Stoffel <john@stoffel.org>
Cc: "Sigurd Karlsbakk" <roy@karlsbakk.net>,
Håkon <hawken@thehawken.org>,
"LVM general discussion and development" <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] Looking ahead - tiering with LVM?
Date: Wed, 09 Sep 2020 22:20:48 +0200 [thread overview]
Message-ID: <dda927d81e53c08da1e5bbd8cc649581@assyoma.it> (raw)
In-Reply-To: <24409.12987.382863.95686@quad.stoffel.home>
Il 2020-09-09 21:53 John Stoffel ha scritto:
> Very true, numbers talk, annecdotes walk...
Sure - lets try to gather some numbers from the data you posted
before...
> sudo lvcache status data/home
> +-----------------------+------------------+
> | Field | Value |
> +-----------------------+------------------+
> | cached | True |
> | size | 806380109824 |
> | cache_lv | home_cache |
> | cache_lv_size | 85899345920 |
You cache device is squarely in the 10x ballpark (ie: it is ~9.39x
smaller than your SSD). Having ~10.64% more space would be nice, but
hardly game-changer.
> | read_hits | 138697828 |
> | read_misses | 7874434 |
You have 94.6% hit rate from your hotspot cache - compare this to an
ideally managed tiered storage, with its 100% (ideal, not reasonable in
real world) hit rate. Does it really change anything?
> | write_hits | 777455171 |
> | write_misses | 9841866 |
And you have an even better ~98.7% write hit ratio. As you have a
mirrored cache device, you should be able to set LVM for using a
writeback cache without risking your data in case of a single cache
drive failure. I suspect this would do wonder with your hit ratio - but
again, testing is the only method to be sure.
Thanks for sharing your data!
Regards.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
next prev parent reply other threads:[~2020-09-09 20:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-02 18:38 [linux-lvm] Looking ahead - tiering with LVM? 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 [this message]
2020-09-09 19:41 ` Roy Sigurd Karlsbakk
2020-09-09 19:49 ` Gionatan Danti
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