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Date:      Thu, 24 Sep 2015 14:37:56 -0400
From:      Paul Kraus <paul@kraus-haus.org>
To:        Dmitrijs <war@dim.lv>
Cc:        FreeBSD Questions <freebsd-questions@freebsd.org>
Subject:   Re: zfs performance degradation
Message-ID:  <2008181C-F0B5-4581-9D15-11911A1DE41B@kraus-haus.org>
In-Reply-To: <56042209.8040903@dim.lv>
References:  <56019211.2050307@dim.lv> <37A37E9D-9D65-4553-BBA2-C5B032163499@kraus-haus.org> <56038054.5060906@dim.lv> <782C9CEF-BE07-4E05-83ED-133B7DA96780@kraus-haus.org> <56040150.90403@dim.lv> <60BF2FC3-0342-46C9-A718-52492303522F@kraus-haus.org> <560412B2.9070905@dim.lv> <8D1FF55C-7068-4AB6-8C0E-B4E64C1BB5FA@kraus-haus.org> <56042209.8040903@dim.lv>

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On Sep 24, 2015, at 12:17, Dmitrijs <war@dim.lv> wrote:

> I also get about 60-70MB/sec via CIFS or ftp, but my aim is to be =
limited by network, so 100MB is wanted.=20

It=92s nice to want things. But be prepared to pay for the things you =
want...

> Or, to understand why it is not possible on my config :)
> But simple dd of=3D/dev/null in the console shows me 110MB/sec=85

dd of anything, but especially of /dev/null is a very poor way of =
measuring anything. Turn on compression and and do that test again.

> iozone gives me the same 100+Mb/sec both on read and write.

What size blocks ? Files ? Random or sequential I/O ? All that matters.

> 2x HGST HDN724040ALE640, 4Tb, 64Mb, 7200.

Consumer NAS drives=85 I have not purchased anything but an Enterprise =
drive for close to 10 years now. The small additional cost is well worth =
the longer (5 year) warranty and better build quality=85 there _is_ a =
difference. Even looking at the specs, the uncorrectable error spec is a =
very good indicator of build quality and these drives are typical 1 in =
10^14 consumer drives. Enterprise drives are typically an order of =
magnitude better, 1 in 10^15.

In your original post you mentioned WD Green drives, also consumer =
grade. In my experience I have seen better performance from WD than =
HGST, with Seagate at the bottom of the ladder. I was comparing all =
Enterprise drives, and even among those offerings there are differences=85=
 the WD RE are noticeable faster than the SE. I look at svc_t as the =
primary metric for _comparing_ drives. I create a simple striped zpool, =
reboot the system to clear counters, then do _lots_ of (typically) =
random I/O, then look at iostat -x and compare svc_t, lower numbers are =
better.

I generally don=92t buy matched drives for mirrors, but different makes =
and models if I can. That way of there is a bad production run I don=92t =
lose all my drives at once. When a drive fails I RMA it under warranty =
and buy 2 more of the same type and capacity, one goes into the server =
and the other sits on the shelf. Eventually I have enough drives to grow =
the zpool and move on.

> For example, yesterday I explored QNAP TS-451
> official site: =
https://www.qnap.com/i/en/product/model.php?II=3D143&event=3D2 (Intel=AE =
Celeron=AE 2.41GHz dual-core processor, 1GB DDR3L, etc)
> and review: http://www.storagereview.com/qnap_ts451_nas_review
> 473euro

They _might_ be fine products, But I don=92t trust my data to =
appliances. _I_ want to control the redundancy.

> Promised performance of the models is about 100Mb/sec, even up to =
200Mb/sec but ok, it's marketing and pretty diagrams ;)

And all the tests were probably done on empty (to start) volumes. You =
can achieve similar numbers with ZFS with similar hardware and LOTS of =
parallel clients.

--
Paul Kraus
paul@kraus-haus.org




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