Topic: RAID choices (HW,SW,RAID5,RAID6)

[dvdsmith]

I think I know the answer to this but I thought I'd ask others opinions.  I am re-purposing an old Dell 1600SC.  It has 5 36gb SCSI drives and an LSI Megaraid 320-1 controller (pulled from another server).  Drive capacity is not an issue, as these are more than sufficient for the intended purpose (PDC + file share).  Current share appoximates to around 10GB, mostly office documents.  What is an issue is hardware vs software RAID.

I'm presented with the following options;

1.  HW RAID5 + spare (LSI controller)
2.  SW RAID5 + spare (Linux software raid)
3.  Buy 2 more drives and allow SME to create a SW RAID6 + spare array.

Based on other posts, I'm leaning toward the first option.  In the past, I've used this particular controller to rebuild a drive in a RAID5 array and was satisfied with the results.  However, I've also replaced drives in SW RAID1 and had good results.  I have no experience with SW RAID5.  Aside from being able to survive a 2 drive failure, are there any compelling reasons to choose SW RAID6 (edit) over HW RAID5 here.  FYI, HW RAID6 is not an option budgetwise.

Thanks, Dave

[Stefano]

I think I know the answer to this but I thought I'd ask others opinions.  I am re-purposing an old Dell 1600SC.  It has 5 36gb SCSI drives and an LSI Megaraid 320-1 controller (pulled from another server).  Drive capacity is not an issue, as these are more than sufficient for the intended purpose (PDC + file share).  Current share appoximates to around 10GB, mostly office documents.  What is an issue is hardware vs software RAID.

be sure your controller is supported by SME/CentOS/RH and be sure you'll find another one, identical in the future.. if raid controller dies, you need another one with the same firmware to recover your data

I'm presented with the following options;

1.  HW RAID5 + spare (LSI controller)
2.  SW RAID5 + spare (Linux software raid)
3.  Buy 2 more drives and allow SME to create a SW RAID6 + spare array.

SW raid 6 eats many cpu cycles.. on the other hand you can syurvive 2 hd failure

Based on other posts, I'm leaning toward the first option.  In the past, I've used this particular controller to rebuild a drive in a RAID5 array and was satisfied with the results.  However, I've also replaced drives in SW RAID1 and had good results.  I have no experience with SW RAID5.  Aside from being able to survive a 2 drive failure, are there any compelling reasons to choose SW RAID6 (edit) over HW RAID5 here.  FYI, HW RAID6 is not an option budgetwise.

Thanks, Dave

hw raid 5 will be faster than sw raid 6.. much faster IMHO

[larieu]

My personal choice is also 1.

not really because of the slightly higher CPU utilisation in SW RAID but also your HW RAID is a good choice and you'll have some tools directly on hardware to rebuild one broken HDD

I had several problems with access to old data on even one HDD install with SME server which is "already prepared" to RAID
(problems only caused because I forgot to take all data from the old system and I kept only the HDD)

and frankly speaking I sow more HDD dead than controllers
and after 1 year you'll not be able to find an IDENTICAL HDD
I was not only one time forced to replace all HDD on one installation because one old HDD passed away
I never experienced in Hardware raid problems to change one by one all HDD

as I told it will be my personal choice
an you must see if your controler is in the CentOS list of supported ones

[dvdsmith]

Thanks everyone, I feel better now about my choice.  I did some quick searching, and there appear to have been drivers for my controller since at least RHEL3.  In any case, I'll do a test setup and see how it behaves when I pull a drive etc.  RAID6 sounded nice but the negatives are greater than benefits in this case.  As for matching replacement drives, extact matches are still available on ebay.  I'll probably pick a couple up from a reputable source just in case.

Thanks again.

[Stefano]

search for megaraid.. I remember some troubles with it

[dvdsmith]

search for megaraid.. I remember some troubles with it

Yeah, there was one post regarding a problem with one of the earlier driver versions, but that was back in RHEL3.  Being as we're on RHEL5 on SME8beta, I'm going to test it out and see what happens.