Date: Sat, 12 May 2007 09:29:12 +0200 From: Peter Schuller <peter.schuller@infidyne.com> To: Bakul Shah <bakul@bitblocks.com> Cc: freebsd-current@freebsd.org, efinley@efinley.com Subject: Re: ZFS the perfect FS? if only... Message-ID: <46456CC8.30909@infidyne.com> In-Reply-To: <20070510224605.C05365B5A@mail.bitblocks.com> References: <20070510224605.C05365B5A@mail.bitblocks.com>
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This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig75932908D1A3AE9B4B5020E1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable > You can do something like this: >=20 > zpool create foo raidz2 dev0 dev1 dev2 dev3 > zpool add foo raidz2 dev4 dev5 dev6 dev7 >=20 > The new devices are in a different raidz2 group but but *all > of the space* will be used for any filesystem on this pool -- > isn't this good enough and if not, why? Isn't it obvious? You waste less diskspace. In the above setup you are only using half your diskspace and depending on what you need it for you might aswell have been using a mirror... Often having two parity drives can be more important than the ratio of parity vs. non-parity. That is, just because one chose to start with a 4 disk raidz2, it does not mean that moving to an 8 disk raidz2 is not consistent with the redundancy goals/requirements chosen initially. Also, if you DO want 50% parity, a single raidz2 with 8 drives with 50% parity is more resilient to failures than 2x4 raidz2 since any 4 drives can fail whereas in the latter case any 2 drives can fail, or up 4 drives if they happen to be the right drives. (I am aware of the "approximately 7 drives" maximum for a raidz/raidz2, which does not really come into play in this case.) > Not worth it Most definitely worth it in many situations where performance is just not the goal. So what if it takes a week to perform the operation, as long as the array is not degraded during this timewindow. --=20 / Peter Schuller PGP userID: 0xE9758B7D or 'Peter Schuller <peter.schuller@infidyne.com>' Key retrieval: Send an E-Mail to getpgpkey@scode.org E-Mail: peter.schuller@infidyne.com Web: http://www.scode.org --------------enig75932908D1A3AE9B4B5020E1 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.3 (FreeBSD) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFGRWzRDNor2+l1i30RCE4eAJ9cE8cWEG1FuCI6MZCbnjRrtjtyMACeJrdo lfP5Uyi3vs548iMt3v2MOUw= =Ugy4 -----END PGP SIGNATURE----- --------------enig75932908D1A3AE9B4B5020E1--
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