Date: Thu, 18 May 2017 17:53:23 -0400 From: Mark Saad <nonesuch@longcount.org> To: kc atgb <kisscoolandthegangbang@hotmail.fr> Cc: "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org> Subject: Re: Different size after zfs send receive Message-ID: <58A6B47B-2992-4BB8-A80E-44F74EAE93B2@longcount.org> In-Reply-To: <DBXPR05MB157C1956B267EA6BE59F570A0E40@DBXPR05MB157.eurprd05.prod.outlook.com> References: <DBXPR05MB157C1956B267EA6BE59F570A0E40@DBXPR05MB157.eurprd05.prod.outlook.com>
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Hi kc=20
This has to do with how data blocks are replicated when stored on a raidzN=
. Moving them to a mirror removes replicated blocks . This is way over simp=
lified but imagine you store a file of 10gb on a raidz1 . The system splits t=
he file into smaller chunks; of say 1mb , and stores one extra chunk for eac=
h chunk that us striped around the raidz1 . Storing on a mirror is just writ=
e the chunk once on each disk . However with a mirror since you only see 1/2=
the number of disks you never see the extra chunks in the used field .=20
Hope this helps .=20
---
Mark Saad | nonesuch@longcount.org
> On May 18, 2017, at 3:36 PM, kc atgb <kisscoolandthegangbang@hotmail.fr> w=
rote:
>=20
> Hi,
>=20
> Some days ago I had a need to backup my current pool and restore it after p=
ool destroy and create.=20
>=20
> The pool in my home server is a raidz1 with 4 disks. To backup this pool I=
grabbed two 4TB disks (single disk pools) to have a double backup (I have j=
ust one
> sata port left I can use to plug a disk).=20
>=20
> The whole process of backup and restore went well as I can say. But lookin=
g at the size reported by zfs list make me a little bit curious.=20
>=20
> storage/datas/ISO 3=
5420869824 381747995136 35420726976 /datas/ISO
> storage/datas/ISO@backup_send =
142848 - 35420726976 -
> storage/datas/ISO@backup_sync =
0 - 35420726976 -
>=20
> b1/datas/ISO 354393=
08800 2176300351488 35439210496 /datas/ISO
> b1/datas/ISO@backup_send 9=
8304 - 35439210496 -
> b1/datas/ISO@backup_sync =
0 - 35439210496 -
>=20
> b2/datas/ISO 354393=
08800 2176298991616 35439210496 /datas/ISO
> b2/datas/ISO@backup_send 9=
8304 - 35439210496 -
> b2/datas/ISO@backup_sync =
0 - 35439210496 -
>=20
> storage/datas/ISO 3=
5421024576 381303470016 35420715072 /datas/ISO
> storage/datas/ISO@backup_send =
142848 - 35420715072 -
> storage/datas/ISO@backup_sync =
11904 - 35420715072 -
>=20
>=20
> storage/usrobj 5=
819085888 381747995136 5816276544 legacy
> storage/usrobj@create =
166656 - 214272 -
> storage/usrobj@backup_send =
2642688 - 5816228928 -
> storage/usrobj@backup_sync =
0 - 5816276544 -
>=20
> b1/usrobj 56750=
81728 2176300351488 5673222144 legacy
> b1/usrobj@create 1=
14688 - 147456 -
> b1/usrobj@backup_send 17=
44896 - 5673222144 -
> b1/usrobj@backup_sync =
0 - 5673222144 -
>=20
> b2/usrobj 56751=
88224 2176298991616 5673328640 legacy
> b2/usrobj@create 1=
14688 - 147456 -
> b2/usrobj@backup_send 17=
44896 - 5673328640 -
> b2/usrobj@backup_sync =
0 - 5673328640 -
>=20
> storage/usrobj 5=
820359616 381303470016 5815098048 legacy
> storage/usrobj@create =
166656 - 214272 -
> storage/usrobj@backup_send =
2535552 - 5815098048 -
> storage/usrobj@backup_sync =
11904 - 5815098048 -
>=20
> As you can see the numbers are different for each pool (the initial raidz1=
, backup1 disk, backup2 disk and new raidz1). I mean in the USED column. I h=
ave
> nearly all my datasets in the same situation (those with fixed data that h=
ave not changed between the beginning of the process and now). backup1 and b=
ackup2
> are identical disks with exactly the same configurations and have differen=
t numbers. I used the same commands for all my transfers except the name of t=
he
> destination pool.=20
>=20
> So, I wonder what can cause these differences ? Is it something I have to w=
orry about ? Can I consider this as a normal behavior ?=20
>=20
> Thanks for your enlightments,
> K.
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