Date: Fri, 27 Feb 2015 09:38:55 +0100 From: marco ardito <ardito@apiform.to.it> To: freebsd-doc@FreeBSD.org Subject: question about zfs doc Message-ID: <54F02D1F.6080808@apiform.to.it>
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Hi, I was reading your zfs guide (excellent : until now, I wasn't able to really undertand how cool zfs is. Thanks, another point to freebsd (not yet user, thoough), but I found a section which could be missing one paragraph, maybe? here https://www.freebsd.org/doc/handbook/zfs-term.html#zfs-term-vdev ...is RAID-Z2 description missing? /"RAID-Z/ - ZFS implements RAID-Z, a variation on standard RAID-5 that offers better distribution of parity and eliminates the "RAID-5 write hole" in which the data and parity information become inconsistent after an unexpected restart. ZFS supports three levels of RAID-Z which provide varying levels of redundancy in exchange for decreasing levels of usable storage. The types are named RAID-Z1 through RAID-Z3 based on the number of parity devices in the array and the number of disks which can fail while the pool remains operational. In a RAID-Z1 configuration with four disks, each 1 TB, usable storage is 3 TB and the pool will still be able to operate in degraded mode with one faulted disk. If an additional disk goes offline before the faulted disk is replaced and resilvered, all data in the pool can be lost. In a RAID-Z3 configuration with eight disks of 1 TB, the volume will provide 5 TB of usable space and still be able to operate with three faulted disks. Sun^(TM) recommends no more than nine disks in a single vdev. If the configuration has more disks, it is recommended to divide them into separate vdevs and the pool data will be striped across them. A configuration of two RAID-Z2 vdevs consisting of 8 disks each would create something similar to a RAID-60 array. A RAID-Z group's storage capacity is approximately the size of the smallest disk multiplied by the number of non-parity disks. Four 1 TB disks in RAID-Z1 has an effective size of approximately 3 TB, and an array of eight 1 TB disks in RAID-Z3 will yield 5 TB of usable space." Thanks! -- *Marco Ardito* Responsabile Servizi Informatici Api Formazione s.c.r.l. Via Pianezza 123, 10151 - TORINO Tel: +39-0114513123 Fax: +39-0114551150 - +39-0114515075 Mail : ardito@apiform.to.it <mailto:ardito@apiform.to.it> Web : http://www.apiform.to.it ------------------- [Ai sensi e per gli effetti della Legge sulla tutela della privacy (L. 196/2003), questa mail è destinata unicamente alle persone sopra indicate e le informazioni in essa contenute sono da considerarsi strettamente riservate. E' proibito leggere, copiare, usare o diffondere il contenuto della presente mail senza autorizzazione. Se avete ricevuto questo messaggio per errore, siete pregati di rispedire la stessa al mittente. Grazie]
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