SAN vs. Local disk.


 
Thread Tools Search this Thread
Top Forums UNIX for Beginners Questions & Answers SAN vs. Local disk.
# 1  
Old 02-15-2019
SAN vs. Local disk.

I am in the market looking to purchase a new E950 server and I am trying to decide between using local SSD drives or SSD based SAN. The application that will be running on this server is read-intensive so I am looking for the most optimal configuration to support this application. There are no other servers or applications that will use this SAN (if I decide to go that route.) The deciding factor to me is Performance regardless of the hardware cost (granted I don't want to pay for something I end up not using.) SAN or local SSD (both running RAID 10)? This is really the question I am trying to answer before I pull the trigger and complete this purchase. Any insights from this community is greatly appreciated.


If it helps, here is the configuration I am currently looking at for a server with Local Storage. NVME disks will be used as boot devices. No Plans to run VIOS or create another LPAR. just one instance supporting one application.

  • 1 9040-MR9 IBM E950 Power 9 Rack Mount Server, includes:
  • 4 EPWR IBM 8 Core 3.6/3.8 P9 Processor (32 Core Total)
  • 32 EPWV 1 Core Processor Activations (32 total)
  • 4 EB3M Power Supply - 2000W
  • 4 EM03 Memory Riser Card
  • 32 EM6B 16GB DDR4 Memory Dimms (512GB total)
  • 2 EC5J 800GB NVMe Drives (Boot/OS Drives)
  • 7 ESHU 1.86TB SFF-3 SSD Drives (RAID 10 with one spare)
  • 2 EJ0L PCIe RAID Quad Port Adapter with 12GB cache, 6GPS per port.

Moderator's Comments:
Mod Comment MOD's comment: Kindly use [LIST]...[/LIST]tags for listing items in your posts.
This User Gave Thanks to ikx For This Post:
# 2  
Old 02-25-2019
It all comes down to the homonyms cash & cache.

How much is you budget for cache? That's the key really. SSD is slightly slower than cache.

For write operations, you would have to balance off the time to commit the update to real disk (even if it is SSD) between the two. if you pass the update to a SAN, it will respond very quickly to say that you have written it, but it will actually write the data in its own time. The update is cached for write but you can continue. There will be cache batteries for power loss before it's really written. For local disk, it depends. Does the RAID controller have a good cache allocation and would therefore behave in the same way? If not, you (the operating system) must ensure that the write is complete before you proceed (costing CPU Sys time I think) and that can confusingly make local IO slower.

You have, of course, stated that this is a read intensive server so your other thing to consider is cache/RAM in the server. The server will fill up with the data you read in normally anyway, but if you wish, you could pre-read the data to give it a head-start. Beware that you need to have lots of memory for this else you will just drop it again. You can just do a find for the files of data you want and cat them to /dev/null so that they get read. Is 512Gb sufficient for your data? You don't say how much you have.



I hoe that my thoughts help,
Robin
# 3  
Old 02-25-2019
Quote:
Originally Posted by ikx
I am in the market looking to purchase a new E950 server and I am trying to decide between using local SSD drives or SSD based SAN. The application that will be running on this server is read-intensive so I am looking for the most optimal configuration to support this application. There are no other servers or applications that will use this SAN (if I decide to go that route.) The deciding factor to me is Performance regardless of the hardware cost (granted I don't want to pay for something I end up not using.) SAN or local SSD (both running RAID 10)? This is really the question I am trying to answer before I pull the trigger and complete this purchase. Any insights from this community is greatly appreciated.
There are a few more points to consider IMHO:

1) disks (regardless which technology) will over time malfunction and need to be replaced. There is some effort involved in such a replacement. SAN systems have usually ways to - more or less - "effortless" replacing disks built in because they usually are used to deal with a lot of disks and the chance that one disk malfunctions rises with the number of disks involved. You might want to do some risk calculation based on how often on average you expect a disk to break (there is usually a "MTBF" - "meantime between failure" number available), how long you expect the change to take and how much a downtime of the expected duration will cost.

2) SANs and local disks do differ in the way they are attached to the system. Local disks may use SCSI or the "M.2" interface. Notice that you cannot have several local (SSD-) disks attached via M.2. SAN, onthe other hand, may use a FC-connection or even several FC-connections in parallel (FC-drivers allow this for redundancy as well as load-balancing). The capacity of such FC-connections may by far exceed the speed of local disks. On the other hand you will need not only a SAN but also a FC-switch (Brocade are the most wide-spread) and the administration ("zoning") will be more complicated.

3) SANs - if set up with this in mind - may add redundancy and thus high-availability to the system. Again, it depends on the system, its purpose, etc.. to calculate properly the risk of it failing for some amount of time. Calculate how much it would set you back to have the system offline for: 1 hour / 1day / 1 week and this will give you an idea how much money spent on preventing these kinds of desasters is worthwhile.

4) SAN systems for themselves are rather expensive. To alleviate this they become cheaper and cheaper (in comparison to local disks) the more you virtualise and the more systems use it. So, a plan to buy a SAN system for a single system only might be on the expensive side but with a expectation of adding other systems using it too the costs may still be reasonable. So you may want to rethink your immediate problem in a more gobal context.

5) Notice that for a system optimised for speed you need an adequate backup solution. For this you also need a disaster scenario plan to estimate what the costs could be and hence how much the prevention may cost. Then you know how fast a recovery needs to be and therefore which technologies you need to employ to get that speed. You can use a SAN also for snapshots (perhaps quickest way of recovering a "point in time"), very fast medium to put an online backup to, only then migrating it to slower media like tapes and similar solutions. You might want to take that also into consideration.

I hope this helps.

bakunin
Login or Register to Ask a Question

Previous Thread | Next Thread

10 More Discussions You Might Find Interesting

1. AIX

SAN Disk Appearing double in AIX

Hello Folks, I have directly connected my IBM Pseries AIX machine to SAN Storage I have a dual port Fibre Channel Adapter Connected both fiber ports to SAN Box IBM DS4500 Controller A & Controller B Using IBM DS storage manager client 10 -- created one logical disk and assigned to a... (18 Replies)
Discussion started by: filosophizer
18 Replies

2. Red Hat

Sharing SAN disk with multiple severs

Hi , I had a requirement to share a san disk between two rhel severs. I am planning to discover the same disk in two rhel nodes and mount it. Is it a feasible solution? and what kind of issues we may encounter mounting same disk in two OS's parallel ? (2 Replies)
Discussion started by: nanduri
2 Replies

3. UNIX for Advanced & Expert Users

Oracle VM / T3 SAN or Local for LDOMS?

I have some T3's we just purchased and we are looking to carve these up into LDOMS's. Just wondering if anyone can give me a quick run down or pro / cons on SAN vs local internal for the LDOM itself. These will external SAN storage for their applications. (0 Replies)
Discussion started by: jlouki01
0 Replies

4. Solaris

I/O Error on SAN Disk

Hi, I have a production solaris 10 SPARC system (portal). Yesterday legato/Networker gave an I/O Error on one of the files on its SAN mounted disk. I went to that particular file on the system, did an ls and it showed the file. However, ls -l did not work and it said IO error. ... (6 Replies)
Discussion started by: Mack1982
6 Replies

5. UNIX for Dummies Questions & Answers

SAN and Disk I/O ... do we care?

Hi all, My main function is as a DBA. Another person manages the server and the SAN. I just want to know if I should be worried about high disk I/O or is it irrelevant as the I/O "load balancing" will be "taken care" of by the SAN? For example, I have hdisk1-5 and I can see that there are... (2 Replies)
Discussion started by: newbie_01
2 Replies

6. Filesystems, Disks and Memory

SAN Disk w/o Cluster

Scenario: I've got 2 M5000's connected to a 9985 SAN storage array. I have configured the SAN disks with stmsboot, format and newfs. I can access the same SAN space from both systems. I have created files from both systems on the SAN space. Question: Why can't I see the file created... (3 Replies)
Discussion started by: bluescreen
3 Replies

7. Solaris

SAN disk failure

hi all, have a solaris 9 OS and a SAN disk which used to work fine is not getting picked up by my machine. can anyone point out things to check in order to troubleshoot this ?? thanks in advance. (3 Replies)
Discussion started by: cesarNZ
3 Replies

8. AIX

hard disk and san

Hello everyone I got several aix boxes with aix 5.3 I got a ibm san ds4500 My question is How can I do a match between my disks on aix and the san? I try to do a match with the LUN but for example. In my san I got several 1 LUN and on one of my aix box I got this If I type lscfg... (4 Replies)
Discussion started by: lo-lp-kl
4 Replies

9. Filesystems, Disks and Memory

disk errors with san snapshot

so we have a solrais 9 system attached to an HP SAN. we are using sssu to do snap clones every hour. the only problem is the we get write errors on the solrais system every time we do a snap. from /var/adm/messages Apr 21 14:37:48 svr001 scsi: WARNING:... (0 Replies)
Discussion started by: robsonde
0 Replies

10. AIX

AIX disk less with SAN

Hi All, I have mirrored SAN volume on my B80 rootvg. Can I just remove the mirror and "Remove a P V from a V G" and it will be a diskless AIX? Is that going to boot on SAN rootvg volume? Thanks in advance, itik (3 Replies)
Discussion started by: itik
3 Replies
Login or Register to Ask a Question