yaribhas
2 Iron

Hotspares

Jump to solution

Is it a good idea to have 600GB Hotspares for 300GB disks?

I know the rebuild time will be greater but generally I am just curious if many have done this and should I create more than 1 HS per 30 disks if I am going to use 600GB HS for 300's

Labels (1)
Tags (4)
0 Kudos
1 Solution

Accepted Solutions
RRR
5 Tungsten

Re: Hotspares

Jump to solution

If you only have 300GB drives in production to be protected by hot spares, you should be using 300GB drives. Why use 600’s ? The only reason I can think of is that a new 600 might be cheaper than a 300. Both will do the job and I don’t even see a reason why a 600 should be slower.

1 Per 30 is ok, but consider this: how many drives have you EVER encountered that were broken in the SAME array AT THE SAME TIME ? I’ve had 2 drives at the same time just recently and I’m doing storage now since 2004.

For DMX (years ago) EMC said (I think) 3 HSs for the first 100 and 1 more for every hundred extra drives. Clariion drives don’t break any sooner than DMX drives.

0 Kudos
10 Replies
DanJost
2 Iron

Re: Hotspares

Jump to solution

As long as the rotational speed is the same, I don't think it'd be any slower.  If you have a mix of 300 and 600GB drives in your system you can certainly use 600GB drives as hotspares.

Dan

RRR
5 Tungsten

Re: Hotspares

Jump to solution

If you only have 300GB drives in production to be protected by hot spares, you should be using 300GB drives. Why use 600’s ? The only reason I can think of is that a new 600 might be cheaper than a 300. Both will do the job and I don’t even see a reason why a 600 should be slower.

1 Per 30 is ok, but consider this: how many drives have you EVER encountered that were broken in the SAME array AT THE SAME TIME ? I’ve had 2 drives at the same time just recently and I’m doing storage now since 2004.

For DMX (years ago) EMC said (I think) 3 HSs for the first 100 and 1 more for every hundred extra drives. Clariion drives don’t break any sooner than DMX drives.

0 Kudos
Highlighted
jimkunysz
2 Iron

Re: Hotspares

Jump to solution

a 300Gb can definitely  spare to a 600GB. the iops on the disk are identical so no loss in performance. also, it won't take any longer for a 300GB to spare to a 600GB as compared to a 300GB. There is still only a max of 300GB of sizing to write, even though the target is larger.

In regards to having fewer hotspares in a frame because there just doesn't seem to be enough failures to warrant the recommended numbers of spares, I consider that to be a poor decision.

As drive sizes have gotten larger, the rebuild times have also increased in time. It will take longer for a 600GB to spare out versus a 300GB drive thus the risk of a double-disk fault is increased. If we talk SATA, I always do a minimum of Raid6 plus a hotspare per dae (in the NS/Clariion model, VNX may be different).

Plan for the worst expected condition and enjoy the uptime.

jps00
2 Iron

Re: Hotspares

Jump to solution

Keep in mind, its the 'in-use' capacity of the drive that is rebuilt, not the entire drive.  Although, you may have the drive's capacity 100% utilized.

Generally, using hot spares of the highest rpms and largest, in-use capacity is prudent.  That avoids the performance hit of getting a slower hot spare, temporarily in the RAID group.

0 Kudos
yaribhas
2 Iron

Re: Hotspares

Jump to solution

All we have are FC disks and our resident wants just 600GB disks as HS's.

I just checked and the rotational speeds are the same for 300's and 600's. If I understood all of you right I think we are ok here.

What do you guys think about Raid groups with (6+1) configuration. I know it is going to be slower than (4+1) but will save us disk space

And how hard will it be to convert to a thin allocation in the future if we move in raid group direction now?

Thanks!

0 Kudos
dynamox
6 Gallium

Re: Hotspares

Jump to solution

6+1 will be faster, more drives support more iops/MB/s.  With virtual provisioning you want to add a lot of drives at once because currently you can't restripe new storage in a pool. So if you burn all of your drives on traditional raid groups, it will be tough in the future.

0 Kudos

Re: Hotspares

Jump to solution

Rebuild time will be the same as long as the 600GB disk is the same RPM. FLARE only rebuilds the portions of disk that have data (ie: bound LUNs). So if you only used the first 25% (75GB) of the 300GB disks, it will only rebuild 75GB of data to the spare. This also means that if you have 600GB drives that are not full, FLARE can rebuild onto smaller disks (300GB, 450GB, etc) and sometimes will do that even if a larger disk is available.

0 Kudos
yaribhas
2 Iron

Re: Hotspares

Jump to solution

I am probably wrong but does (6+1) config mean that there is going to be extra I/O's used up for writing parity to more disks than (4+1)?

By that theory iIf we wanted good performance than we might be better of going with Raid group(13+1). with enough HS's right?

Why is (4+1) recommended configuration by EMC if these other configurations give better performance.

And HS's are not permanent replacement in clariion correct?

0 Kudos

Re: Hotspares

Jump to solution

6+1 is a reasonable RG Size and the performance difference will be minimal.

If you want to move to thin later, you will need to create a pool on different disks, then you can LUN migrate the LUNs into the pool. LUN Migration into a Thin LUN in a pool will perform space reclaim and turn the LUN into a Thin LUN automatically.

0 Kudos