Follow-up install questions

[William A. Mahaffey III]

On 10/15/15 11:23, kpneal at 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 at hiwaay.net <mailto:wam at 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

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	"The M1 Garand is without doubt the finest implement of war
	 ever devised by man."
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