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Date:      Wed, 3 Jul 2013 11:56:05 +0000
From:      Ivailo Tanusheff <Ivailo.Tanusheff@skrill.com>
To:        Alexandr <shuriku@shurik.kiev.ua>, "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org>
Subject:   RE: Whole disk ZFS or -a4k partition
Message-ID:  <8afaecbe0f764963b57fac7743f483bc@DBXPR07MB064.eurprd07.prod.outlook.com>
In-Reply-To: <51D3ED4F.5030102@shurik.kiev.ua>
References:  <51D3ED4F.5030102@shurik.kiev.ua>

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Hi,

I can give you my point of view:

Which zpool do you refer to? Still I would align both pools - on SSD becaus=
e you will have a boot code anyway.=20
What I would do on SSD is to use:
gpart add -b 34 -s 94 -t freebsd-boot <ssd drive>

The second thing I would get in mind Is the swap - I would not use a ZFS fo=
r that, had a lot of issues with similar setup and taking into account that=
 ZFS uses a lot of RAM you may become to situation when you want to swap da=
ta to use RAM for ZFS functionality, related to the swap volume on the ZFS =
subsystem, which is a deadlock scenario.
So I would advise you to create swap partition on the SSD and use this part=
ition in the system.
gpart add -t freebsd-swap -s 4G  -l ssd-swap <ssd drive>
gpart add -t freebsd-zfs -l ssd-zfs <ssd drive>

This will solve you the alignment, swap issues and etc.

About the second drive - there are two issues: may you need to replace the =
disk and will you need additional swap in some case.
Just because future is unsure I would recommend to again use 4K align, to c=
reate a similar SWAP partition and DO NOT use it on the system and use gnop=
 for the 4K sizing:
gnop create -S 4096 /dev/gpt/disk0
zpool create zroot /dev/gpt/disk0.nop
zpool export zroot
gnop destroy /dev/gpt/disk0.nop
zpool import zroot

This way you will solve:
-  the 4K issues, if you have any;
- the replacement issues, if you get a disk with smaller sector count;
- in case you have some swap issues/needs, you will be able to issue swapon=
 /dev/gpt/... and temporary increasethe swap, but not using this all time y=
ou will not decrease performance of the system in normal days.

Best regards,
Ivailo Tanusheff


-----Original Message-----
From: owner-freebsd-fs@freebsd.org [mailto:owner-freebsd-fs@freebsd.org] On=
 Behalf Of Alexandr
Sent: Wednesday, July 03, 2013 12:22 PM
To: freebsd-fs@freebsd.org
Subject: Whole disk ZFS or -a4k partition

Hello, community!

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:

1. Do I need to create a 4k aligned partition on HDD for zfs pool or best t=
o use a whole disk?
2. Where the best place for swap - ssd or hdd? SSD is much faster, but with=
 limited write life cycle.
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