# Which is better LVM2 or EVMS?

## gtl4407

Hi All,

 I have two machines running Gentoo linux, one I have using LVM2 and the other EVMS. I have to say I feel more comfortable with LVM2, because I know it better. I installed EVMS to understand it a bit  (almost a year ago) but In reality I have never had time to get into it.  So my questions is, is it really worth me persevering with EVMS, or should I just migrate the  machine with EVMS to LVM2 - or visa versa?? What is your experience with either/both.

Thanks a lot!!

Regards,

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## Moriah

I have used lvm[1] and lvm2 as well as evms.  

Evms is nice, and powerful, and maybe just more than you or I need right now.  I do think it is the way things will be going in the long run.  Evms is a great unifier of things like partitions, raid, lvm, etc.  It works by plugins, so it is readily extensible to accomodate new things.  

My biggest problem with evms is that it is too darn automatic for what I was trying to do.  If I take a drive offline, evms renumbers all the remaining drives at the next reboot, which messes me up royally.  

Being a guy who likes to shift my own gears, I fell back to naked raid and lvm2 for my application, but evms also has features for clustering, so if you need to do the big stuff, you might be better off with it.

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## waverider202

Internally, EVMS just uses LVM.  The nice thing about EVMS is that it can uniquely identify an object (region/disk/segment/volume).  That means, if you have en evms volume on /dev/hdb, and one day, you switch things around, and that disk is now /dev/hdc, then evms will still bring up all your devices.  Another nice feature is the software Bad Block Relocation segment manager.  BBR increases the reliability of a hard disk.

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## Moriah

Yes, but whenever I am doing things where stuff like evms counts, I am doing some kind of raid, and if I take drive[n] of a raid array offline, and then stick a new drive in its place, this recognition works against me instead of for me.  If I needed volume recognition to keep track of where individual drives were, it would be a nice feature.

Likewise, BBR only helps with single drives, or non-redundant raid-0, or linear appending.  When the raid structure provides redundancy, BBR only slows things down.  If a drive is acting sick, the raid redundancy will keep it going, and I want to know about it quickly so I can replace the faulty drive.  I am a big fan of raid-1 with 3-way mirrors, so even when a drive fails or is otherwise taken offline, I still have redundance.  I see no sense in having a spare drive in a raid-1 situation sitting offline waiting to go online when a failure occurs, as during reconstruction, another failure will kill you.  With 3-way mirroring under raid-1, you can have a drive offline and still have the protection of redundancy.

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## waverider202

If you take out drive[n] of a raid, and replace it, evms will not automatically add it to the raid.  You fire up the evms program, add in the object, then you are good.

As far as redundancy, a drive "acting sick" usually means the drive is reporting i/o errors.  In a raid[1/4/5] situation, as soon as i/o errors are detected, the hard disk is completely booted from the raid.  If you stick bbr in there, then the hard disk i/o errors (bad blocks) will effect the bbr buffer.  It will take longer for the hard disk to get kicked out of the raid.  I can't afford to replace 250gb hard disks every time one of them gets a bad block.

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## Moriah

I was at Sam's Club this past Saturday for something totally unrelated, but I always check their disk prices.  A 250 GB drive was $99.00 US, so I *CAN* afford to replace them rather than risk the whole drive going kaput on me.  Besides, I always sign up on the manufacturer's web page for the extended warranty for $15.00 US.  That way, if the drive fails within 3 years, I just stuff a spare in its slot and send the bad drive back for depot exchange.  Takes about a monh, but well worth it if you have very many raids built from 250 GB drives.   :Smile: 

PS Best Buy had an *EXTERNAL* USB 500 GB drive for only $299.00 the same day.  I wanted to price internal SATA drives, but they gotta be cheaper.  The 400 GB drives were only $200.00 US.

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