Microsoft Azure
Disk & File Storage — Managed Disks & Azure Files
Choose between block, file and object storage, and size a disk for the IOPS it actually needs.
Three shapes, and picking wrongly is either slow or expensive.
The managed disk is the drive inside one machine. Azure Files is the shared network drive the office mounts. Blob Storage is the post room — you hand things in and collect them by reference.
Key Concepts
1
Managed Disk block one disk, one VM. A virtual drive.
Azure Files file an SMB/NFS share, many VMs at once.
Blob Storage object an HTTP API. Not a filesystem.2
A managed disk attaches to one VM and lives in one zone, so a zone failure takes it with it. Snapshots and Azure Backup are what make it recoverable.
3
The disk tiers.
Ultra sub-millisecond, IOPS and throughput set independently
Premium SSD v2 modern default: pay for capacity, IOPS and
throughput separately, no fixed tier sizes
Premium SSD fixed tiers (P10..P80) -- size determines IOPS
Standard SSD dev/test, light production
Standard HDD backups, archival4
Premium SSD v2 is the one to mention. On Premium SSD you had to buy a larger disk purely to reach the IOPS you wanted; v2 decouples them, so a small fast disk is possible and usually cheaper.
5
Bursting hides problems. Smaller Premium disks burst above their baseline for a while using credits. A workload that fits inside the burst in testing falls off a cliff in production when the credits run out — a genuinely common incident.
6
Azure Files is for shared access. SMB or NFS, mountable from many VMs and from on-premises, with AD authentication. Use it for shared uploads, legacy applications expecting a drive letter, and lift-and-shift. Do not use it as a database volume; the latency shows.
7
Azure NetApp Files is the high-performance option when Files is not fast enough and the application genuinely needs a POSIX filesystem.
8
Redundancy is chosen at the storage account for Files and Blobs: LRS within a datacentre, ZRS across zones, GRS to a paired region. Managed disks are LRS or ZRS.
9
Host caching is free performance. ReadOnly for a data disk that is read-heavy, None for write-heavy logs. Getting it backwards slows things measurably, and it costs nothing to set correctly.
10
What the interviewer is probing.1. "Why is Premium SSD v2 usually better than Premium SSD?" Probing: the IOPS coupling.
Stalls: "It is newer." Moves up: Premium SSD fixes IOPS by tier size, so you oversized to get
speed; v2 sells capacity, IOPS and throughput separately.
11
2. "Your disk was fast for an hour then slowed sharply. Why?" Probing: burst credits.
Stalls: "Noisy neighbours." Moves up: smaller Premium disks burst above baseline on credits;
once exhausted, performance drops to the baseline.
12
3. "When would you use Azure Files rather than a disk?" Probing: shared access. Stalls: "For
bigger storage." Moves up: when several machines must read and write the same files, or an
application expects a mounted share — not for a database, where the latency shows.
13
4. "What does host caching do and when is it wrong?" Probing: free performance, set correctly.
Stalls: "It speeds everything up." Moves up: ReadOnly suits a read-heavy data disk; None suits
write-heavy logs, and getting it backwards measurably costs throughput.