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Impact of adding a PS4000E to an existing PS4000XV
Hello
New to the forums here.
I have a PS4000XV with 16 600GB SAS in RAID-10. Users are happy with performance I just need more capacity so I am about to purchase a second member. This environment is growing steadily so rather than add another 3U/3.6TB usable shelf I am exploring the viability of adding a PS4000E with 1TB or 2TB SATA.
So my main questions are:
1) Will I slow performance if I mix SAS and SATA in a Pool (I need 2500IOPS < 20ms response)
2) Is anyone actually doing this? (even though Dell tell me the EQL auto-tiers)
3) Assuming it auto-tiers how can I calculate my hot blocks to understand whether I could expect my hot data to fit into my SAS tier (if I understand the tiering correctly)
Thanks in advance for your time to read this.
Hayden
DELL-Joe S
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729 Posts
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March 17th, 2011 08:00
Hayden,
If you have one pool, and you want to add two different drive technologies (i.e., SAS and SATA) into the same pool, each member would need to be configured with unique raid policy (example: Member_A_SAS is Raid 10, and Member_B_SATA is Raid 50).
I agree with Don, IMO run them in seperate pools.
Joe
DELL-Joe S
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March 14th, 2011 07:00
Hayden,
Hi, I'm Joe with Dell EqualLogic.
For the best practices when configuring a storage pool:
1. Do not mix arrays with different drive speeds within a single pool unless they are running a unique RAID policy
2. Do not mix arrays with different drive technologies (SATA, SAS, SSD) within a single pool unless they are running a unique RAID policy.
3. Do not mix arrays with different controller speeds (1GbE, 10GbE) within a single pool unless they are each running unique RAID policies.
Take a look at this document for further details: for the best practices when configuring a storage pool:
http://attachments.wetpaintserv.us/rP8fcTzwQW9Kth8bzSLtUw610645
And this one for basic pool design (Section 3.2):
http://attachments.wetpaintserv.us/K2rieX6WedD_OVUmA2Xhmw1894185
Regards,
Joe
hurricanehaydo
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March 16th, 2011 23:00
Thank you for your prompt response Joe. I am confused by 'unless they are running a unique RAID policy'? Is this unique to the group or unique to the members? To clarify - would it therefore be supported and a good solution to mix two arrays with a single pool and with the SAS array running in RAID-10 and the SATA array running RAID-5 OR do they both need to run the same RAID?
Regards
Hayden
mfkelly_tx
31 Posts
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March 17th, 2011 05:00
Running arrays that are not identical in the same pool is fine if you set the RAID type differently. Running arrays that are not identical in the same pool is bad if you set the RAID type the same.
Anonymous
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March 17th, 2011 08:00
It's not quite as simple as that.
You absolutely can run the same RAID type on multiple members in the same pool. What's typically not suggested is mixing SAS/SATA in the same pool period. There's an asymmetry on how IO is handled. Also, since data is spread between members in proportion to their relative sizes, SAS arrays tend to have larger drives. So more data will be on those members vs. SAS. But it you want more space and more IO at a given RAID level you can put them the same pool.
Also in regards to the 4000 series specifically, there are additional limits on those arrays regarding number of iSCSI connections among other limits. So putting 4000's into different pools doubles the connection count.
If you're running 4000's in different RAID levels, IMO, run them in separate pools. Especially if using ESX or Hyper-V. Since they tend to use up allot of iSCSI connections. If you put them in the same pool at different RAID levels, setting RAID type preference on the volumes would be recommended.
-don