That was very detailed And quite good On 1/19/09, Lisa Kachold wrote: > > > > > > > > I have built and maintained linux production servers under both hardware > RAID 5 on HP MSA's, > and hardware RAID 1+0 on both HP Proliant's and Dell 2950's/1950's (with a > variety of software disk management [depending on the server farm > standards]). > > I have also configured LVM and md under SATA or iSCSI systems in both RAID 5 > and RAID 10. > > [I have also built Solaris servers under RAID 5/RAID 10 using SVM, and later > replaced with N1 over multi-path I/O on Sun 2450's (zfs); and worked with > NetApps/Redhat (xfs).] > > I am a proponent of md/LVM over hardware RAID because Linux md does not > handle bad block relocation; I love simply rebuilding the array, especially > since drives heat up, get torged by power, and are simply not build with QA > these days. > > Since disk is so incredibly cheap these days (by comparison in your lower > level [non enterprise] solution), the popularity of RAID 5 is offset by the > full mirror and rebuild protection of RAID 1+0. > > Here's the technical descriptions of each level: > > RAID 0 is not redundant at all but offers the best > throughput of all levels here. Data is striped across a number of > drives so read and write operations take place in parallel across > all drives. On the other hand if a single drive fail then > everything is lost. Did I mention backups? > RAID 1 is the most primitive method of obtaining redundancy > by duplicating data across all drives. Naturally this is > massively wasteful but you get one substantial advantage which is > fast access. > The drive that access the data first wins. Transfers > are not any faster than for a single drive, even though you might > get some faster read transfers by using one track reading per > drive. > > Also if you have only 2 drives this is the only method of achieving > redundancy. > RAID 2 and 4 are not so common and are not covered > here. > RAID 3 uses a number of disks (at least 2) to store data > in a striped RAID 0 fashion. It also uses an additional redundancy > disk to store the XOR sum of the data from the data disks. Should > the redundancy disk fail, the system can continue to operate as if > nothing happened. Should any single data disk fail the system can > compute the data on this disk from the information on the redundancy > disk and all remaining disks. Any double fault will bring the whole > RAID set off-line. > > RAID 3 makes sense only with at least 2 data disks (3 disks > including the redundancy disk). Theoretically there is no limit for > the number of disks in the set, but the probability of a fault > increases with the number of disks in the RAID set. Usually the > upper limit is 5 to 7 disks in a single RAID set. > > Since RAID 3 stores all redundancy information on a dedicated disk > and since this information has to be updated whenever a write to any > data disk occurs, the overall write speed of a RAID 3 set is limited > by the write speed of the redundancy disk. This, too, is a limit for > the number of disks in a RAID set. The overall read speed of a RAID > 3 set with all data disks up and running is that of a RAID 0 set > with that number of data disks. If the set has to reconstruct data > stored on a failed disk from redundant information, the performance > will be severely limited: All disks in the set have to be read and > XOR-ed to compute the missing information. > RAID 5 is just like RAID 3, but the redundancy > information is spread on all disks of the RAID set. This improves > write performance, because load is distributed more evenly between > all available disks. Parity data is rotated across all disks so > total net storage equals all disks minus 1. > RAID 6 is similar to RAID 5 except that there is twice the > redundancy and the array can survive 2 failed drives. > Parity data is also rotated across all disks so > total net storage equals all disks minus 2. > > > There are also hybrids available based on RAID 0 or 1 and one other > level. Many combinations are possible but I have only seen a few > referred to. These are more complex than the above mentioned > RAID levels. > RAID 01 combines striping with duplication > as mirrored arrays of striped arrays > which gives very high transfers combined with fast seeks as well as > redundancy. The disadvantage is high disk consumption as well as > the above mentioned complexity. > Also a single disk failure turns the array into RAID 0. > RAID 1+0 combines striping with duplication > as striped arrays of mirrored arrays > which gives very high transfers combined with fast seeks as well as > redundancy. The disadvantage is high disk consumption as well as > the above mentioned complexity. > > When you are scrounging disk against money you are sure that two of your > disks are not going down, so choose not to use 4 disk 1+0. But believe me, > THEY DO, and that's it! Also RAID 1+0 out performs in a fast good way. > What use is a huge cheap slow system? > > Full discussion available here that includes a complete analysis of md > systems, and all the types of data loss that generally occur. > > http://linas.org/linux/raid.html > > www.Obnosis.com | http://wiki.obnosis.com | http://hackfest.obnosis.com > (503)754-4452 > PLUG HACKFESTS - http://uat.edu Second Saturday of Each Month Noon - 3PM > > Date: Mon, 19 Jan 2009 07:30:08 -0700 > From: mark@phillipsmarketing.biz > To: plug-discuss@lists.plug.phoenix.az.us > Subject: Re: Looking For RAID Hardware/Software Advice > > Eric > Thanks for the summary, and thank-you to everyone for their ideas. > Based on NewEgg prices, here is some more information: > > Option A > Single Disk IDE Drive - 500 GB and backups, keep OS on existing drive = > $69.99 > > Use existing controller and just add another drive. No redundancy > > Option B > RAID10 with 500 GB backup capacity and redundancy, keep OS on existing drive > = $179.97 > 2 500 GB SATA2 Drives, new SATA2 controller > > > Option C > RAID10 with 750 GB backup capacity and redundancy, keep OS on existing drive > = $239.97 > Two 750 GB SATA2 Drives, new SATA2 controller > > Option D > RAID5 with 1,000 GB backup capacity and redundancy, keep OS on existing > drive = $239.97 > > Three 500 GB SATA2 Drives, new SATA2 controller > > I am leaning towards Option C based on less power consumption with fewer > drives. However, I have to rethink my budget... > After some more reading, I am a little confused about the debate between > RAID5 and RIAD10. I am interested in the group's opinions on which is better > - RAID 5 or RAID 10 and why? What experiences have you had regarding > installation, maintenance, and fixing problems? I am running Debian testing. > > Thanks! > Mark > On Sat, Jan 17, 2009 at 6:35 AM, Eric Shubert wrote: > > Mark Phillips wrote: > >> I am running out of room for my backups. I use backuppc and I have > >> almost filled a 150GB drive with backups from 7 computers, and I need to > >> add another 2 computers to the set. I have an old Dell Poweredge 1300 > >> server (Pentium III 550 Mhz, 500 MB RAM, PCI 33.3Mhz) that I could turn > >> into a backup server. I am looking for suggestions/thoughts on how to > >> set this up. I need to keep the cost down as much as possible; under $150. > >> > >> My initial thoughts: > >> > >> * Keep current 72 GB drive for OS (debian testing, about 68% full) > >> * Add two 500 GB SATA drives and a PCI SATA controller ~$130 > >> * Software RAID and LVM for the two drives > >> * Move current 150 GB of backups to the RAID > >> * Backuppc now runs on this machine and slowly fills up the RAID > >> > >> My questions: > >> > >> 1. Should I keep the 72 GB drive for OS, or put it on the RAID? > >> > >> 2. I can add another CPU (P III 550 MHz) processor to the box - is it > >> worth the effort to find one? I found one source for $5/CPU, I just need > >> to find the heat sink and mounting hardware. Will this improve >> performance? > >> > >> 3. The box has a built-in SCSI 68-pin Ultra2/wide bus/controller, but > >> SCSI drives are more expensive, at least from a cursory google search. > >> Is this correct? I don't think I can use SCSI drives within my budget > >> constraint. > >> > >> 4. Would upgrading the memory to 1GB improve performance - top shows: > >> Mem: 646676k total, 639300k used 7376k free, 64548k buffers > >> This would add another ~$60 to my cost. > >> > >> 5. Should I look at hardware RAID cards - they seem very cheap, so > >> perhaps software is better? > >> > >> 4. Does this plan make sense, or is there a better way to proceed for > >> about the same cost? > >> > >> Thanks! > >> > >> Mark > >> > > > > Good replies, all. To sum things up, I think a SATAII PCI card (2 or 4 > > port) and 2 drives is all the HW you need to add to the backup box you > > currently have. Set up the drives with SW RAID-1 (mirrored) and you're > > good to go. Migrate the data to the raid device, and keep the OS on the > > existing drive. > > > > With KeepItSimpleStupid in mind, I recommend using RAID-1 as opposed to > > RAID-5. With the price of drives these days, the additional space you > > get with RAID-5 isn't worth the headache you'll get when there's a > > problem. With RAID-1, each drive can be mounted (and used) individually > > if necessary. Not so with RAID-5. > > > > -- > > -Eric 'shubes' > > > > --------------------------------------------------- > > PLUG-discuss mailing list - PLUG-discuss@lists.plug.phoenix.az.us > > To subscribe, unsubscribe, or to change your mail settings: > > http://lists.PLUG.phoenix.az.us/mailman/listinfo/plug-discuss > > > > Windows Live™: Keep your life in sync. Check it out. > _________________________________________________________________ > Windows Live™ Hotmail(R): Chat. Store. Share. Do more with mail. > http://windowslive.com/explore?ocid=TXT_TAGLM_WL_t1_hm_justgotbetter_explore_012009 -- Sent from my mobile device A mouse trap, placed on top of your alarm clock, will prevent you from rolling over and going back to sleep after you hit the snooze button. 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