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Solid State Drive for Windows 2008 Domain Controller

Martin Gerlach
Martin Gerlach used Ask the Experts™
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I am putting together a Server which will act as a Domain Controller. I chose a HP ProLiant DL360 G7 Server, HP gives me an option for a 60GB SSD drive (HP 60GB Hot Plug 3G SATA SFF MDL Solid State) which costs around $1000.00.

I used SSD drives for Desktop systems and I am really happy with it. I am expecting much better performance and a much longer drive lifetime for the server using a SSD drive. Would you agree or do you see any downsides besides the high price tag? I requested more specific's about the drive from HP but I assume it's a top of the line Intel Drive. I'll post the drive details once HP get's back to me.

Please give me your thoughts.

 
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Commented:
Traditionally the response time for a DC request is not as important as a request on the desktop. The request is limited by the performance of the network more than of the server. So basically the performance gain is not as high as you would expect. For a single request that is!
When you are running a highly active Windows network, and your users start complaining about the responsiveness of your DC, it is time to consider performance boosts on the server side. In that situation a SSD will improve the amount of requests per second the server can deliver. Note however that in a system showing performance degradation, the improvement will only last as long as no other bottleneck is presented. Again the networking bandwidth is the first candidate for being a bottleneck. Too low estimated memory will also be one of the first sins of decreasing performance figures. Then comes the disk storage and finally the (average!) processing time.
This at least is my experience. Of course each workload has its own charateristics and your may differ from someone else's.

So my conclusion on you question is: Only if you need the better disk performance you must choose the SSD. If not then opt for a traditional and much cheaper SAS drive. About the life time: In many cases the change from Windows 2003 to Windows 2008R2 or virtualization projects force the replacement of the server, not the outdated hardware!

A second remark I like to make is: If your (single!) DC is getting to the limits, don't find a solution in faster hardware, but invest in a secondary DC to spread the load. Even two cheaper servers will perform better than a more pricy single server! If only one server dies ...

Jan Meijer
DavidPresident
Top Expert 2010
Commented:
First, here is some generic info ... the garbage cleanup logic of a SSD (called TRIM), which tells the SSD what blocks you no longer need, will never kick in unless your O/S has modified drivers; you have JBOD & the SSD supports it.  W/o TRIM the SSD gets slower over time and wears out sooner (big picture, not trying to turn this into a multi-page doc)

I assume you do not have a pure JBOD config, so HP doesn't have a controller/SSD combination which can take advantage of TRIM ...
But, in this case, not an issue.   The architecture & firmware of this particular SSD has a large reserved area, and the firmware works quite well cleaning up the garbage.  It is designed not to require this garbage collection.

The top of the line Intel SSD is NOT ACCEPTABLE for you, because it is behind a SMARTArray, so TRIM won't work, so if you are looking for something that will serve you for years to come, don't buy it.  (There is more to it then just TRIM)

If you can plug a SSD into the native SATA ports, and bypass the expander & smartarray, then you can use Intel, OCZ, or any other SSD and probably come out way ahead.  SSDs are not infallible, they have bit rot, unrecoverable reads and fail too.   As this is a domain controller then you need to mirror (using native NTFS).  

But if you go the HP way, you can mirror in the controller and will be OK.

So for 3rd party - software Mirroring, and attach the SSDs to non-RAID SATA ports.   For pure HP, you can do that too, but if you want to attach to SMARTArray, then it will work w/o trim.




Commented:
I forgot he most imporatant argument against SSD:

Even SSD's will fail eventually. So in normal production environment that means you must implement SSD in RAID1. Now compare the costs to the 73 GB HDD's...

Jan Meijer
Martin GerlachConsultant

Author

Commented:
Thanks for the feedback, I'll actually get two new DC's replacing the two old ones. So in your opinion there is no downside of setting up a SSD drive for the DC's?
DavidPresident
Top Expert 2010

Commented:
Yes, I see a downside, you are throwing money away, unless your DC is on an offshore oil rig or somewhere else that gets so much vibration that you are afraid a mechanical disk won't live long.

Buy 3 x 73 GB drives, set for RAID6.   It will be slower, but you will have dual redundancy.  I can't imagine disk I/O ever being a bottleneck for a DC, unless you are doing other things with it.
Martin GerlachConsultant

Author

Commented:
@dlethe - Sorry i saw your post after i wrote my comment. I'll have to read up on this a bit more to understand what you are talking about. Do you know any good resources to get up to date with this stuff?

Commented:
Considering dlethe's remarks and my remarks: When I was to make the choice, I'd opt for HDD's not the SSD. Only use SSD (and HDD too) with redundant devices available for important production servers.

Jan Meijer
They are massively over priced. Check out OWC Mercury Pro, OCZ Vertex 2 and Runcore Kylin drives after you buy the base from HP.
DavidPresident
Top Expert 2010

Commented:
innovationcc - Not aware of some good tutorials, there is a lot of stuff you can find with google.  I've got NDA developer agreements with some SSD & RAID/controller manufacturers , so have to be careful about only mentioning what is "common knowledge".  

The biggies
1. Real-world performance can easily vary +/- 500% for some SSD manufacturers, even with a single SATA disk on Win7, fresh out of the box.  Vendor/product specific algorithms that optimize for different I/O sizes, and sometimes even data itself.  (I.e, internal SSD data compression.  speed on a sparse file with lots of zeros can be over 5X faster then a random number data stream)

2. The garbage collection.   Unlike HDD, where a 1 stays a 1 forever, or until you change it .. a SSD needs to know when you are no longer going to need that 1.   A command that is referred to as TRIM is really one of several commands that allows an O/S and file system to say when it doesn't need that 1, or that file any more.   Win7 does this by detecting if you have a SSD and querying it to determine the features ...

3. But put a disk behind a RAID controller, then the O/S has no idea where the data is physically located, so it won't work.   The work-around is mostly, go without, but there are some tricks that I'm not going to get into from non-disclosure reasons.   Suffice to say, if you want RAID or  something other than NTFS + LINUX JBOD, then you can go with some new LSI products.   Or you can go with HPs product (which is OEMed) and firmware is set up to not need this TRIM.  

4. Beyond that, there are parameters with wear leveling, which are just way to much to go into, suffice to say, pound some SSDs for few days or a week, and then you may find a situation where you are only writing at 7-8 MB/sec. (W/o this automated TRIM).

5. TRIM is best if automated, i.e, when you delete a file, the O/S and driver tells the SSD that those blocks are unused, so the SSD can do background processing to clear up the space.  Performance and ratio of 1s to 0s and what happens depending on reads vs writes or seq vs random I/O is pretty significant for SOME SSD products  

Commented:
I would recommend using RAID1. The performance loss of RAID6 on such a small disk is not worth the investment. RAID6 theoretically offers double redundancy, but that is only intended for large disks (1 TB and more) simply because the time to rebuild a RAID configuration is aking long on those devices. It has no real ma=eaning for redundancy. A RAID1 73 GB arrya taka about one hour to rebuld, add another hour for problem detection and replacement of the drive you have on stock, you'll be at risk for two hours in case a disk failure occurs.

Had you been running a RAID1 on  1 TB disks, it would cost you over 24 hours to reconstruct the array. Then it comes handy to have a secondary redundancy option available.

Let alone that the DL 360 does not support  RAID6 on the standard controller

Jan Meijer
DavidPresident
Top Expert 2010

Commented:
P.S.  Don't let this TRIM thing scare you off, it depends on life cycle, and other variables. Even if you have a SSD that has horrible garbage collection, and needs the TRIM or it just hits a brick wall, then your usage patterns may make you immune.  

The trick is to really look at specs, understand your usage.   Not all SSDs are appropriate for all environments.  I will tell you that performance characteristics between the Vertex 2 and the non-OEM version of the HP product, in a RAID5 config by a good 200%, more if you were trying to make one look better than the other by "cooking" the benchmark & configuration.

If you bench, use REAL data, not a benchmarking program, unless that program lets you create data & files and mixes percentage of 1s vs 0s. SSDs care about penalties for writing 1s over 0s.  Mechanical drives dont

DavidPresident
Top Expert 2010

Commented:
On the RAID6, if we are talking drive redundancy, I agree, but RAID6 is much more valuable protection against unreadable blocks.   Let's say you had DISK#1 that has a few unreadable blocks..    In a RAID1, you lose disk #0,  it tries to rebuild, hits the bad block.  You have data loss.  If bad block is at logical block #0.  Your system won't even boot.

All it takes is one bad block on a disk that did NOT fail, and you are screwed.   R6 protects against that.  Do a search and see how many people report failed rebuilds due to bad blocks, and ask for a data recovery firm.  I've gotten enough points out of those cries for help alone  to get a Tshirt :-
DavidPresident
Top Expert 2010

Commented:
RAID recoveries easily range from $5K - $20K.   Is it worth the risk?  Certainly not as much if you have a full current backup, but humans do stupid things & hardware breaks.

Commented:
@dlethe Agreed on the RAID5 portion of RAID6, but lets not dwell on RAID 6 here: the DL360 does not support it!

Jan Meijer
Martin GerlachConsultant

Author

Commented:
I just got news that i might have to use one of the DC's as a file server as well, which changes things. I got this configuration in mind:

RAID Controller
HP P410 with 1G Flash Back Cache Smart Array  Controller

Drives
5 x 600GB HOTPLUG  SAS 15k -   Raid6 (OS, ADS, Production Files, Databases)
3 x 2TB HOT PLUG      SAS 7.2k - Raid5 (Archive File)

Or should i do a RAID 0+1 for the 600GB drives? It will still be more then enough storage left doing that. I am not sure which RAID is faster 5 or 0+1
DavidPresident
Top Expert 2010

Commented:
There are some corner-cases, but 0+1 will be faster on 99% of the things you do.
Martin GerlachConsultant

Author

Commented:
Great. One last question. Will I only be able to setup one RAID configuration per RAID controller or is it possible to configure multiple raid setup? Or does it depend on the controller i'll use?
DavidPresident
Top Expert 2010

Commented:
You'd have to look at the specs for the controller you have, I don't know them w/o researching.  Many let you have more than one volume, but not all.

Commented:
Sorry WET forced me to call it a day ...

As I said before, the HP controller, i.e. the P410 has no standard RAID6 support (except if the SAAP function is included). That will make the RAID0+1 option a good alternative. The P410 DOES let you set up more thaan one array, so your idea to set up two arrays will work out okay. However, RAID0+1 requires an even set of disks,

FYI, the SAAP support is optional and depends on the DL360 model choosen:

Entry Models HP Smart Array P410i/Zero Memory Controller (RAID 0/1/1+0)
Base Models HP Smart Array P410i/256 MB Controller (RAID 0/1/1+0/5/5+0)
Performance Models HP Smart Array P410i/1G FBWC Controller (RAID 0/1/1+0/5/5+0)
Efficiency Models HP Smart Array P410i/Zero Memory Controller (RAID 0/1/1+0)
Available Smart Array upgrades: 256MB, Battery kit upgrade (to add BBWC to the 256MB Memory
option), 512MB BBWC, 512MB FBWC or 1G FBWC and Smart Array Advanced Pack (SAAP)

So persuade the boss to obtain the SAAP function, use RAID6 on the 600 GB drives, RAID5 on the 1TB drives (RAID6 requires at minimum 4 drives). Or (if storage is over sized, opt for  4x 600 GB and 4x 1000 GB, then use RAID6 on both. For the non-filer DC, just use a simple RAID1 on two smaller disks.

Jan Meijer
Martin GerlachConsultant

Author

Commented:
I choose the P410 with 1G Flash Back Cache Smart Array Controller and i'll also get the SAAP option. There are two different ones:

HP Smart Array Advance Pack and
HP Hot Plug Advance Pack

Can you tell me the difference?

Commented:
To my knowledge, but hey I am not an HP rep, there is only a HPAP for the B110 controller, so I could not tell the difference. That one only supports 6 disks, which is not what you want,
unless the two DL360 boxes are totally different configured.
But if you happen to have an HP order number i guess i could look it up.

Jan Meijer
Martin GerlachConsultant

Author

Commented:
Great feedback. Thank you.