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Date:      Sat, 25 May 2013 11:44:59 -0400
From:      Paul Kraus <paul@kraus-haus.org>
To:        Michael Sierchio <kudzu@tenebras.com>
Cc:        saeedeh motlagh <saeedeh.motlagh@gmail.com>, freebsd-questions <freebsd-questions@freebsd.org>
Subject:   Re: file corruption solution (soft-update or ZFS)
Message-ID:  <9F319856-E79D-49F5-A0C9-3650DDC0C740@kraus-haus.org>
In-Reply-To: <CAHu1Y704ufB_ie00hZrXw84WE5tT-b6t0O1uDjy69AbD7y9g-g@mail.gmail.com>
References:  <CAN+S=WC0ThjT6ox9YdUsAb6++f=+qfCLuct_tN=jsr3KYTezaw@mail.gmail.com> <alpine.BSF.2.00.1305230554360.98184@wonkity.com> <CAN+S=WDGdL5ZabOGp+rBshjmrd9so5Q=wMc5sfDGuEAZxLe3+g@mail.gmail.com> <alpine.BSF.2.00.1305230629560.98184@wonkity.com> <CAHu1Y704ufB_ie00hZrXw84WE5tT-b6t0O1uDjy69AbD7y9g-g@mail.gmail.com>

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On May 23, 2013, at 11:09 AM, Michael Sierchio <kudzu@tenebras.com> =
wrote:

> On Thu, May 23, 2013 at 5:33 AM, Warren Block <wblock@wonkity.com> =
wrote:
>=20
>> ..
>=20
>> One thing mentioned earlier is that ZFS wants lots of memory.  4G-8G
>> minimum, some might say as much as the server will hold.
>>=20
>>=20
> Not necessarily so - deduplication places great demands on memory, but =
that
> can be satisfied with dedicated cache devices (on SSD for performance =
and
> safety reasons).  Without dedup, the requirements are more modest.

The rule of thumb for DeDupe is 1GB physical RAM for every 1TB of =
capacity. The issue is that the DeDupe metadata table must live in the =
ARC for good performance. The discussion I have seen on the ZFS lists =
indicates that L2ARC is not really adequate for this, so adding cache =
devices (SSD's) don't really help.

On the other hand, you can use ZFS without DeDupe with as little as 2GB =
of total system RAM (depending on what else the system is doing). In my =
experience, the amount of RAM depends on the amount of I/O not the =
amount of storage. I find between 1GB and 3GB space for the ARC is =
adequate.

--
Paul Kraus
Deputy Technical Director, LoneStarCon 3
Sound Coordinator, Schenectady Light Opera Company




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