Date: Thu, 15 Oct 2015 16:14:37 -0453.75 From: "William A. Mahaffey III" <wam@hiwaay.net> Cc: FreeBSD Questions !!!! <freebsd-questions@freebsd.org> Subject: Re: Follow-up install questions Message-ID: <562015F3.5020306@hiwaay.net> In-Reply-To: <20151015161649.GA61524@neutralgood.org> References: <561F9FAC.9080308@hiwaay.net> <CA%2BtpaK1v=e8avEBEuHJKpcRnPXpqes7iBBgpsmgOpkWv=ah8pQ@mail.gmail.com> <561FAEE7.2030505@hiwaay.net> <20151015161649.GA61524@neutralgood.org>
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On 10/15/15 11:23, kpneal@pobox.com wrote:
> On Thu, Oct 15, 2015 at 08:54:57AM -0453, William A. Mahaffey III wrote:
>> On 10/15/15 08:40, Adam Vande More wrote:
>>> On Thu, Oct 15, 2015 at 7:42 AM, William A. Mahaffey III
>>> <wam@hiwaay.net <mailto:wam@hiwaay.net>> wrote:
>>>
>>> Pursuant to ongoing issues trying to install FreeBSD 9.3R on my
>>> Myth-TV box, I have some questions about provisioning another box,
>>> also w/ 9.3R. That box is AMD A-10 APU based, w/ 8X 1 TB 2.5"
>>> HDD's. Given the problems I am having getting the (smaller,
>>> simpler box) going. I am pondering using ZFS on the larger box. To
>>> that end, I have a couple of questions. ZFS supports (man page)
>>> 'unmirrored pools'. Is that tantamount to striped RAID ? If so,
>>> what sort of I/O performance can I look for there ? There was a
>>> lengthy thread a few weeks ago on ZFS & performance. I (think I)
>>> recall someone saying they used a bunch of 1-HDD vdevs to get some
>>> semblance of good I/O performance w/ a RAIDZn configuration, is
>>> that (additional layer of config) actually required ? My man page
>>> says vdev's can be single devices or 'a collection of devices',
>>> with devices being disks (individual HDD's ?), files, mirrors, or
>>> raidz's. Are those mirrors necessarily ZFS mirrors, or can they be
>>> gmirrors ? I am interested in maximizing the size of the storage
>>> pool available, & the best I/O performance I can get. This box
>>> will be backed up across the LAN onto other boxen, so I am
>>> worrying less about HDD reliability & more about performance & max
>>> available GiB's/TiB's. TIA & have a good one.
> Don't mix ZFS with gmirror. If you are going to use mirrors then let
> ZFS handle it.
OK, roger that.
>
> ZFS stripes across vdevs. A vdev consisting of a single drive is allowed.
> You can add and remove mirrors from a single drive vdev. There are _no_
> single drive RAIDZ* vdevs.
>
> A pool consisting of nothing but single-drive vdevs would indeed be an
> "unmirrored pool". But if a single drive fails you lose the contents
> of the entire pool.
Roger that, that's why this box will be backed up across the LAN (daily
rsync, weekly compressed tar), I'm good w/ the risk, I just want as many
GiB's of storage & as much I/O performance as reasonably possible, &
within the bounds of capability of the technology, which I don't always
have a good grip on (viz my problems w/ the smaller MythTV box) :-/ ....
>
> As for performance, a RAIDZ* vdev will read and write at about the speed
> of a single drive. A mirror vdev will write about the same speed unless
> you have lots of drives in the mirror. In that case a mirror vdev's
> writes will be slower the more drives you put in the mirror. But a mirror
> vdev's _reads_ are supposed to scale with the number of drives in the
> mirror.
OK, roger that on the mirrored read, any idea about unmirrored
reads/write ? I could imagine both scaling (possibly weakly, but scaling
nonetheless) w/ # of drives, no ?
>
>>> Why is speed such a concern for you? A single SATA is easily enough
>>> to read and write multiple 1080p streams concurrently.
>>>
>>> What do you have against white space? It's too painful to read further.
>> & WTF about white space ?
> Your writing does look like a wall of text. If you split it into multiple
> paragraphs with no indenting and a blank line between them then it will
> be much easier to make it to the end of one of your posts.
Fair enough, I have heard for years that I write far too 'literarily',
i.e. in prose, rather than technically .... I'll look into a 12-step ;-)
....
--
William A. Mahaffey III
----------------------------------------------------------------------
"The M1 Garand is without doubt the finest implement of war
ever devised by man."
-- Gen. George S. Patton Jr.
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