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From: Phillip Susi <phill@thesusis.net>
To: Chris Murphy <lists@colorremedies.com>
Cc: Cedric.dewijs@eclipso.eu, Linux-RAID <linux-raid@vger.kernel.org>
Subject: Re: What is the best way to combine 4 HDD's and 2 SSD's into a single filesystem?
Date: Tue, 19 Jan 2021 14:27:55 -0500	[thread overview]
Message-ID: <87ft2w67hh.fsf@vps.thesusis.net> (raw)
In-Reply-To: <CAJCQCtTT+_2F2EFUz=juOn2YG+ZOu2gmNx1Qwu2wp6273T9DNA@mail.gmail.com>


Chris Murphy writes:

> A
>
> HDD1+SSD1=>
>                             Btrfs raid1 profile for metadata, raid0 or
> raid1 profile for data depending on your risk tolerance
> HDD2+SSD2=>

But then sometimes reads will go to one leg and miss the cache and have
to hit the HDD even though the data is in the ssd cache of the other leg
already.  Therefore, wouldn't it be preferable to keep the mirroring
underneath the cache?  Also having a separate B with the other two HDDs
and using it purely as a backup further halves your storage capacity (
so now only 1/4th ).  Also if one disk gets spun up to satisfy a read,
the next read might go start up the other disk rather than go to the one
that is already running.

I'd say make a raid5 of the 4 HDDs, a raid1 of the the two SSDs, and use
the combined SSDs to cache the combined HDDs.

      reply	other threads:[~2021-01-19 20:03 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-17 20:35 What is the best way to combine 4 HDD's and 2 SSD's into a single filesystem?  
2021-01-17 22:38 ` John Stoffel
2021-01-17 23:32 ` Wols Lists
2021-01-18  1:59 ` Chris Murphy
2021-01-19 19:27   ` Phillip Susi [this message]

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