From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?UTF-8?Q?Micha=C5=82?= Sawicz Subject: Re: Best strategy to incrementally replace smaller HDDs Date: Fri, 09 Sep 2011 16:20:20 +0200 Message-ID: <1315578025.14468.18.camel@michal-laptop> References: <1315565285.2291.25.camel@michal-laptop> <20110909131351.GA25347@cthulhu.home.robinhill.me.uk> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-mH7/mfCPlN9BsdfrxIC7" Return-path: In-Reply-To: <20110909131351.GA25347@cthulhu.home.robinhill.me.uk> Sender: linux-raid-owner@vger.kernel.org To: Robin Hill Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids --=-mH7/mfCPlN9BsdfrxIC7 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Dnia 2011-09-09, pi=C4=85 o godzinie 14:13 +0100, Robin Hill pisze: > On Fri Sep 09, 2011 at 12:48:01PM +0200, Micha=C5=82 Sawicz wrote: >=20 > > Hi all, given the configuration below: > > * 8 x 1TB HDDs > > * 2 x 2TB HDDs > >=20 > From what you cover below, it sounds like you're limited to 10 drives in > total. Is this the case? In the long run - yes, but I can have more temporarily. It's just a physical issue, not controller issue. > > On which I currently have: > > * (10 x 1TB) RAID6 - persistent storage > > * (2 x 1TB) system / temporary storage etc. > >=20 > > I want to replace the 1TB drives for 2TB ones on an as-needed basis, > > what strategy would you recommend? > >=20 > > 1. If I moved to 2TB RAID6 members (using RAID0 on the 1TB drives)= , > > I would need to replace two of the drives just to match current > > capacity. Each next 2TB drive would get me 1TB additional > > capacity (but actually I'd need to replace two to gain > > anything). That sounds to be most future-proof, but most > > expensive. > > 2. If I moved to 2TB RAID5 members, that would reduce redundancy > > but replacing just two would gain me 2TB capacity. Most of the > > above still applies. >=20 > So, for both of these, you're planning on changing to: > * (2 x 1TB) system > * (2 x 2TB) + (3 x 1+1TB) persistent storage Actually no, currently I'm planning to go: * (2 x 1TB) system, * (4 x 2TB) + (2 x 1+1TB) So that's 8TB in RAID6, 10TB in RAID5. I already have 8TB and the only way is up. With RAID6 I'd have to replace at least 4x1TB for 3x2TB initially (one less drive total). > This gives you 6TB persistent storage in RAID6, or 8TB in RAID5. As you > say, replacing 2 1TB drives for 2TB drives (or adding a 2TB drive, if > possible) would give you 8TB in RAID6 again. >=20 > You'll also need to do a backup, rebuild & restore for either of these > solutions. As I mentioned in my previous reply to David, I'm planning to shrink/grow as needed. > In either case, replacing a single drive (assuming you're limited in > total drive count) would not gain any capacity, whereas a pair of drive > replacements would give you a 2TB increase. >=20 > I'd steer clear of RAID5 with 2TB drives - rebuilding a 2TB drive will > present a very large window for total array failure. Yeah, that's why I switched to RAID6 in the first place... > > 3. If I kept to 1TB RAID6 (two on the 2TB drives), I would reduce > > the redundancy to just one drive if it was the 2TB drive that > > failed, but each new drive would gain me 1TB capacity and I onl= y > > need to replace one-by-one. This sounds like the cheapest, but > > worst possible approach. > >=20 > Losing a single 2TB drive would lose 2 partitions, wiping out all > redundancy. You're only needing to rebuild 1TB before you're back to > partial redundancy though, so you're less prone to read failures than > with RAID5 above. A second 2TB drive failure during recovery of either > partition will cause total array failure though. >=20 > Replacing a single 1TB drive would gain you 1TB in space. >=20 > There's also no need to do a complete wipe & restore - you can just > replace the drive and recover onto the new one. >=20 > Performance will be worse (particularly during recovery) as you're > always seeking between the two partitions. >=20 > Personally, I'd go with RAID6 on 2TB partitions. It is more expensive, > but I think the performance and redundancy benefits outweigh the costs. That's the direction I'm leaning to as well. Thanks a lot for the comments! --=20 Micha=C5=82 (Saviq) Sawicz --=-mH7/mfCPlN9BsdfrxIC7 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iQIcBAABAgAGBQJOaiCkAAoJEGnv7NPGHSZFNOAQAK0ON40k6dADMoYxdAnXuW8v aAqYuZAi1+nGdHTWdIO38/VOUkcGViVGVKyGehPBZvg5g+8jYI2Q5++ETcRfid/7 lEVrSNno3AxeBTqPtv8u+tfhuPBOZ+Y4NVD8+Z5pW2RhVKZw25PSul+EpsczC/Y4 KCmCKQK7CiGhH1KF8OHa8h+rYwTVZuyH/IR6pnq4R6kyf6Nj50ez2OXdXwfdekL/ 6hCUSeSMNpB1z/yF5gUOzAiLzmiAg5UDG8Zf5xbzmKLBPsS5GBRl6hv/VOszpOaI RjLlsN9qOLUGhG1UBwF/clUkkULixegJKbBKD3He4j/LzD0+ThqFcZZQpBOaiPUj nXG3fRTm+ldIQvFCAgLUNl0kplZZK4j499sD/8O6uNZhMoafBcxB6Z5LWluPgu+3 gBNIPMYxOc834h00rRdOh39/DVfcOtqSPPXE+FQE0vpbCXT5nI4EWSATZQDWN+65 WPGNEn23ilAKb7mQh30XvEfHd9VGOt0843UmeOcKdiaiUgH4qxn81vZD4y8F1pft MrjGa+6qWYqn+52kGCCwvx8KpaQpjwFsGKoF9zkOidrwtzwpcVuPY316tpUysRME MSt24nccxoCxX2XqKd2kT1W3wiG1lXmXjRcqJUdiXPA+M2vZnwkByMZKAXrbvugF rq6rOqy0drycVL+Jsi+z =+mGN -----END PGP SIGNATURE----- --=-mH7/mfCPlN9BsdfrxIC7--