Date: Wed, 3 Jul 2013 11:46:29 +0200 From: Fleuriot Damien <ml@my.gd> To: Alexandr <shuriku@shurik.kiev.ua> Cc: freebsd-fs@freebsd.org Subject: Re: Whole disk ZFS or -a4k partition Message-ID: <F05806B1-944D-4982-81F5-0893D9F6E0C4@my.gd> In-Reply-To: <51D3ED4F.5030102@shurik.kiev.ua> References: <51D3ED4F.5030102@shurik.kiev.ua>
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On Jul 3, 2013, at 11:22 AM, Alexandr <shuriku@shurik.kiev.ua> wrote:
> Hello, community!
>=20
> I have a laptop with 2 disks - mSATA 32Gb SSD and 500Gb HDD. I plan to
> use SSD as whole disk ZFS pool with root and /usr partitions and 500Gb
> SATA as ZFS pool for /home and /var. My questions are:
>=20
> 1. Do I need to create a 4k aligned partition on HDD for zfs pool or
> best to use a whole disk?
> 2. Where the best place for swap - ssd or hdd? SSD is much faster, but
> with limited write life cycle.
>=20
I advise against using the whole disk for the following reason:
DISK1, manufacturer 1: 3tb (give or take)
DISK2, manufacturer 2: 3tb (give or take MINUS 10 BYTES)
Et voila, you can't use DISK1 with DISK2 because DISK2 is 10 bytes =
smaller and won't fit.
When building RAID arrays, it's recommended to:
- use disks from different manufacturers
- use disks ordered at different times (for example half at T1, half at =
T2)
- shave a few MBs off your disks, so that they all present the same size
Here's an example from my nas at home:
% gpart show /dev/ada6
=3D> 34 5860533101 ada6 GPT (2.7T)
34 6 - free - (3.0k)
40 102400 1 freebsd-ufs (50M)
102440 5860430688 2 freebsd-zfs (2.7T)
5860533128 7 - free - (3.5k)
Notice how the disk presents 5860533101 sectors of 512 bytes.
Also notice how I've shaved off 50mbytes in the first, unused partition.
This way, if I replace a disk later on and the new disk only has, say =
5860533095 512-byte sectors, I can still use it in my pool.
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