LVM
in [Debian]
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From: Stan Hoeppner on 16 Jun 2010 06:50 Boyd Stephen Smith Jr. put forth on 6/15/2010 10:44 AM: > On Tuesday 15 June 2010 04:52:10 Stan Hoeppner wrote: >> Boyd Stephen Smith Jr. put forth on 6/14/2010 10:45 AM: >>> On Monday 14 June 2010 03:11:56 Gerald C.Catling wrote: >>>> Hi Guy's, >>>> I am not a Debian user but I have seen references to LVM here. >>>> I have 3 drives LVM'd to give me 1.3TB of storage space on my server. >>>> The first drive of this set has died. >>> >>> Mostly, when one of your physical volumes is irrecoverably lost, so is >>> any logical volume whose logical extents corresponded to one of the lost >>> physical extents. >> >> This is why one should only use LVM on top of real hardware or software >> RAID or a big SAN LUN. > > You should use LVM on top of whatever you have. It's vastly superior to > partitioning as a way to divide a disk. Even if you do not need to divide a > disk, the adds snapshotting and an on-line migration path above just using the > disk. I meant this in the context of the OP's problem. IIRC, he was using LVM to span the capacity of 3 disks into a single large volume, increasing his failure probability 3 fold. Aggregate the space using RAID so you get some redundancy, then use LVM to carve up the resulting space. Don't use LVM to aggregate space, as it increases the odds of total volume failure. Using LVM to manage space on a single disk is fine. Using it for spanning, with no kind of redundancy, is not wise. -- Stan -- To UNSUBSCRIBE, email to debian-user-REQUEST(a)lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmaster(a)lists.debian.org Archive: http://lists.debian.org/4C18A9F3.6040201(a)hardwarefreak.com
From: Stan Hoeppner on 16 Jun 2010 07:10 Ron Johnson put forth on 6/15/2010 1:50 PM: > On 06/15/2010 01:37 PM, Andrew Sackville-West wrote: > [snip] >> an USB enclosure and use it for backups. Having ~700GB of data with the >> most critical ~400GB backed up is definitely preferable than no > > Geez, I remember when I couldn't fill up a 40_MB_ drive, and before that > when I was in awe of the KayPro 10. > My first computer was a Kaypro PC. No CP/M. This was an IBM XT knock off with a 20MB HD, though faster than the XT, sporting an 8MHz 8088. Taught myself dBaseIII/Fox Pro, Turbo Pascal and Quick Basic on that machine (amongst others), as well as burning many an hour playing Microprose' Gunship with a CH Flighstick. :) Sometimes I miss those simpler times... -- Stan -- To UNSUBSCRIBE, email to debian-user-REQUEST(a)lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmaster(a)lists.debian.org Archive: http://lists.debian.org/4C18B0E9.2080400(a)hardwarefreak.com
From: Boyd Stephen Smith Jr. on 16 Jun 2010 11:40 On Wednesday 16 June 2010 04:43:06 martin f krafft wrote: > also sprach Boyd Stephen Smith Jr. <bss(a)iguanasuicide.net> [2010.06.15.2108 +0200]: > > > Use mdadm for a RAID5 or RAID6 and LVM on top for the remaining > > > cases when you need space and care less about performance. > > > > Use RAID 1/0 in mdadm when you need redundancy, space, and performance. > > > > (Although, IME, RAID 5 is not badly performing.) > > Sure it is, on writes. If you have the right hardware, you won't > notice, but every write takes twice as much work. But not twice as much time, which is what performance is about. When you are writing to two disks in parallel, that has (roughly) the same performance as writing to a single disk and (roughly) twice the performance as writing to two disk serially. I've used RAID 5 for years, both HW RAID and SW RAID. I have never had issues with write speeds. > > RAID 1/0 through mdadm with 4 disks is also better than strictly layering > > the RAID levels. > > Do you have any data to back this up? Fundamentally, the data will > traverse one layer less, but does it actually make a difference? It uses a different layout which spreads reads and writes more evenly across the drives. This results in higher performance on the same number of disk writes. -- Boyd Stephen Smith Jr. ,= ,-_-. =. bss(a)iguanasuicide.net ((_/)o o(\_)) ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-' http://iguanasuicide.net/ \_/
From: Boyd Stephen Smith Jr. on 16 Jun 2010 12:10 On Wednesday 16 June 2010 04:43:06 martin f krafft wrote: > also sprach Boyd Stephen Smith Jr. <bss(a)iguanasuicide.net> [2010.06.15.2108 +0200]: > > > Use mdadm for a RAID5 or RAID6 and LVM on top for the remaining > > > cases when you need space and care less about performance. > > > > Use RAID 1/0 in mdadm when you need redundancy, space, and performance. > > > > (Although, IME, RAID 5 is not badly performing.) > > Sure it is, on writes. If you have the right hardware, you won't > notice, but every write takes twice as much work. > > http://git.debian.org/?p=pkg-mdadm/mdadm.git;a=blob;f=docs/RAID5_versus_RAI > D10.txt;hb=refs/heads/contrib/docs/raid5-vs-raid10 While disks may have gotten cheaper, some people only need 20% (or less, RAID 5 doesn't have to be 5 disks) redundancy instead of the 50%, 67%, or more redundancy provided by RAID 1/0. (Also, RAID 1/0 in mdadm is not just stripes over mirrored pairs OR mirroring over striped sets.) RAID 1/0 does indeed have all the recovery advantages mentioned, and I generally recommend it when you can afford the 50% redundancy. The support for RAID 3 or 4 over RAID 5 at the end is completely without basis, and almost certainly wrong. RAID 5 performs better than RAID 4 and 3 under all conditions and has the same failure cases. Clearly, the author was biased against RAID 5 from the start, which throws suspicion on the anecdotes in the prose. Still, the issues listed about RAID 5 recovery are very real, and should be enough to make one reconsider either spending more to be able to use RAID 1/0 and have the same usable space or using RAID 1/0 and doing with less usable space. > http://git.debian.org/?p=pkg-mdadm/mdadm.git;a=blob;f=debian/FAQ;hb=HEAD#l > 106 The layout used with near=2 is, of course, exactly the same as layering. It is unclear, then, how this can be applied to an odd number of devices, per the man page: "e.g. it is perfectly legal to have an ân2â layout for an array with an odd number of devices" I was under the impression that offset=2 would do better about rotating which pairs were mirrored for a data block. The diagrams show hdd1 being mirrored with hdd2 and hdd4 but not with hdd3; similar with far=2. -- Boyd Stephen Smith Jr. ,= ,-_-. =. bss(a)iguanasuicide.net ((_/)o o(\_)) ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-' http://iguanasuicide.net/ \_/
From: Ron Johnson on 16 Jun 2010 13:20 On 06/16/2010 06:09 AM, Stan Hoeppner wrote: > Ron Johnson put forth on 6/15/2010 1:50 PM: >> On 06/15/2010 01:37 PM, Andrew Sackville-West wrote: >> [snip] >>> an USB enclosure and use it for backups. Having ~700GB of data with the >>> most critical ~400GB backed up is definitely preferable than no >> >> Geez, I remember when I couldn't fill up a 40_MB_ drive, and before that >> when I was in awe of the KayPro 10. >> > > My first computer was a Kaypro PC. No CP/M. Youngster. I had a KayPro II. With, originally, TurboPascal 1.0! > This was an IBM XT knock off > with a 20MB HD, though faster than the XT, sporting an 8MHz 8088. Taught > myself dBaseIII/Fox Pro, Turbo Pascal and Quick Basic on that machine (amongst > others), as well as burning many an hour playing Microprose' Gunship with a CH > Flighstick. :) > > Sometimes I miss those simpler times... > -- Seek truth from facts. -- To UNSUBSCRIBE, email to debian-user-REQUEST(a)lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmaster(a)lists.debian.org Archive: http://lists.debian.org/4C19077E.10301(a)cox.net
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